One For All

One For All (ワン・フォー・オール) is a transferable Quirk, possessed by its current host Izuku Midoriya, and was used by its previous hosts Nana Shimura and All Might.

History
Long ago, a man with a Quirk that could steal Quirks and give them away, forcibly gave his seemingly Quirkless little brother a Quirk that allowed him to stockpile power within his body. However, the little brother already had a Quirk with no effect other than that it could be transferred to others. The little brother's Quirk and the Quirk given to him by his older brother merged and became One For All.

The little brother somehow discovered this. He had a strong sense of justice and he tried to defeat All For One, but given the huge difference in their abilities, the brother failed. The little brother decided to entrust the Quirk to future generations of heroes, hoping that they would cultivate One For All and one day, put a stop to All For One. Few knew the truth about One For All. The Quirk was passed down for nine generations, growing stronger with the passage of time. Currently One For All is one of the most powerful Quirks in existence, although it is quite difficult to master.

Description
All Might explains that One For All is the union of two Quirks: A Quirk that stockpiles power, and a Quirk that could be transferred to others. This mutation was caused by the Quirk, All For One.

One For All allows the host to access power from the previous users of the Quirk. It has not been clarified if the Quirk that stockpiles power simply gains more energy as it is passed on (the first holder could not beat All For One, but a recent holder could, which suggests a power increase) or if it is because other Quirk abilities were imprinted into it as it was passed from user to user, and most believe that the people who use the Quirk use it in different ways.

One For All receives its name from the fact that it can be "inherited" by others; it is 'one' Quirk for 'all' people. Like a torch, it is passed on from person to person. The method of inheritance and transference of One For All is done by the recipient ingesting the current wielder's DNA, as shown with All Might giving Izuku Midoriya his strand of hair to ingest which let the latter inherit One For All.

One For All will not transfer to a new recipient unless its owner wishes for that to happen, thus it cannot be forcibly stolen. For example, the Hero Killer Stain ingested Izuku's blood but did not inherit One For All as Izuku was not even aware of such a condition. As One For All cannot be forcibly removed, it is the only quirk that can be used in combat against All For One, as any user of All For One would simply be able to remove the opponent's quirk to end the fight. However, this does not mean One For All cannot be forcibly passed on.

One For All also seems to alter the user's appearance in different ways. For Toshinori Yagi, it significantly enlarges his muscles and overall body mass to make him look like a completely different person similar to that of a giant. For Izuku Midoriya, usage of One For All causes the empowered part of his body to glow, with vein-like lines crossing through each other. His body also generates crackling green energy that resembles lightning bolts when he activates One For All: Full Cowling. It is unknown what the usage of One For All looked like for its previous handlers, however.

After One For All is transferred to the successor recipient, the predecessor can still utilize the "leftover embers" of One For All, and thus still access its power. However, these leftover embers will not last for long, and the previous One For All will slowly lose their access over the Quirk, resulting in the predecessor losing One For All completely. According to All For One, using these last embers continuously will rapidly increase the loss of the power. After All Might defeated All For One, the embers of One For All were burned out, and he cannot even maintain his muscle form for more than an instant, thus providing Izuku the full power.

Proper usage of One For All requires intense and rigorous training of the body to prevent the successor from being torn apart by the raw power flowing within their body. However, not every wielder is stressed the same, and some can get used to it rather quickly, as noted by Gran Torino, who went straight to actual combat training for All Might, since the latter did not take long to adapt to his then-new powers.

However, it is unclear what the true nature of One For All is. When Izuku was about to lose his match against Hitoshi Shinso, he suddenly felt the presence of multiple people coursing through his body and activated One For All to break free from Hitoshi's control. Izuku theorizes that since his Quirk is the "sacred torch that is passed down through the ages," those people that he felt were the lingering presence of those who had this power before him. He also mentions seeing someone with the same hairstyle of All Might among those who appeared in front of him, indicating that his presence is imprinted on the Quirk. All Might believes that it is just a sign of him being accustomed to One For All, it cannot communicate with the user or vice versa. Nana Shimura had theorized that the Quirk remembers all the wills of the predecessors as part of its power, although it still remains a mystery.

In a rare case, Izuku Midoriya was able to once again experience the traces of One For All, this time more clearly. In his dream form, almost all of Izuku's body is shrouded in what seems to resemble dark flames and his hair glows green. He also saw a memory of the first user of One For All confronting All For One. It is later revealed that the first user had intentionally shown the memory to Izuku. Long after his death, All For One's brother was still aware of Izuku being the ninth wielder of One For All and seems to have helpful intentions towards him. All Might believes that the ability to actually interact with previous users of One For All is exclusive to Midoriya.

With the right amount of stockpiled power, One For All grants its wielder many abilities, the most prominent being an immense strength, superior to that of most strength-enhancing Quirks, that allows one to fire blasts of wind through. It also increases the user's other physical attributes, such as speed and toughness.

Over time One for All has amassed the Quirks of all the users and now Izuku is able to at least use them to an extent. This first showed itself during the joint training session with class 1-B. One of the Quirks of the previous users that manifested itself was Black Whip, a Quirk that reacted to Izuku's anger and feelings of wanting to capture Neito Monoma. Deku has five other quirks to discover and become able to use.

One of the previous holders of One For All explained that seeing the traces is a side effect of the core of One For All itself growing. The original quirk factors that had belonged to previous bearers of One For All had merged with the core of One For All. This previous holder of One For All explained that the core of One For All was concealed by the trait of One For All that stockpiles power and that the core of One For All is growing.

Known Users and Usages
One For All has been bestowed to nine different hosts in total, starting with All For One's younger brother. Alongside the Quirk, its origins and the story between the two brothers have been passed on too, since Toshinori Yagi, the eighth user, knew about them.

Because One For All can only be transferred willingly, it's presumed that each wielder had some form of personal connection with at least their corresponding predecessor and successor. Every host was entrusted not only with the Quirk but also with the duty of using it to stop the evil of All For One. It's currently unknown if every user managed to confront All For One like they were supposed to. Nana Shimura was implied to have been killed by his hands, while her direct apprentice and heir to One For All, Toshinori Yagi, fought All For One at least twice, winning both battles.

The named wielders of One For All so far are only Nana Shimura, the seventh, Toshinori Yagi, the eighth, and Izuku Midoriya, the ninth and current holder. All the previous users of One For All seem to be aware of Izuku being the ninth holder of the Quirk.

All For One's Brother
The first user of One For All was the little brother of a villain who had the Quirk, All For One.

Though small and sickly, he had a strong sense of justice and did not back down from opposing his brother's evil deeds. One For All was formed from the mutation of his innate Quirk, and the Quirk All For One forced upon him. The younger brother attempted to defeat his older brother with his newly merged Quirk (now called One For All), but didn't have the sufficient power to do so.

He then passed One For All down to an unknown successor, in the hopes that someone in the future would eventually stop his evil older brother once and for all, a cycle that continues to this day. Even after his death, the brother is aware of Izuku Midoriya being the ninth wielder of One For All and showed him the events leading to the creation of One For All.

Nana Shimura
Toshinori's predecessor and the seventh successor of One For All.

Little is known about Nana's proficiency with One For All, other than she was not capable to bring down All For One. She mentored a boy named Toshinori Yagi, having transferred One For All to him.

Toshinori Yagi
As world-renowned hero All Might, Toshinori is the eighth owner and a very proficient user of this Quirk.

Throughout his career, Toshinori was regarded as the most powerful hero of all time and remained undefeated. With the goal of being a pillar for society, he put One For All to great use, defeating all sorts of criminals, rescuing countless people from danger and turning himself into a legend.

Toshinori is probably the best-known user of the Quirk, if not one of the most talented. Gran Torino once stated that Toshinori did not take long to adapt to One For All, having been blessed with an extremely resilient body despite being born Quirkless. He was able to control and focus his power into any extremity he chose without recoil.

However, due to an untreatable wound that was inflicted on him by All For One in their first known encounter, he could only utilize his Quirk for three hours straight; any longer and it would strain his body. And if he was forced to employ One For All too much, the time limit for using his Quirk would shorten as a repercussion. After transferring the power to Izuku, his ability to use One For All slowly diminished.

During his second battle with All For One during the League of Villains' hideout raid, Toshinori completely depleted all the remains of One for All from his body in order to defeat the villain, essentially leaving him Quirkless once again. Although he can still transform for an instant, he cannot maintain his muscle form anymore as it causes great strain on his body, reverting back very quickly. Having retired himself from heroic activity thanks to this, Toshinori now dedicates himself to solely assisting Izuku in mastering the power of One For All so that he may become a great hero of his own.

Izuku Midoriya
Izuku was chosen by All Might to become the ninth holder of One For All, after the student had proven himself worthy to inherit the Quirk, having done so by ingesting one of All Might's hair strands. Initially, Izuku could only unleash powerful displays of strength at the cost of gravely injuring his own body, as the ten months of training prior to obtaining the Quirk was about getting him to the point of being able to physically hold One For All without blowing off his own limbs. Despite his lack of training or control, One For All's physical backlash was the first step Izuku needed to overcome in mastering this power.

When Izuku manifests One For All's power, his body starts glowing and emitting sparks, with red-colored, vein-like streams coursing throughout his figure. He first used One For All's full power to destroy a giant villain bot in a single punch at the cost of breaking his arm and both his legs.

Izuku eventually came up with a way to minimize damage to himself by focusing One For All's power into his fingers individually. Later, he started subconsciously holding back the power of One For All against living beings. From this point on, Izuku began learning on how to properly modulate the output of his Quirk more effectively.

By focusing One For All in certain portions of his body, he can limit the Quirk's power to avoid breaking his bones. He showcased this in both encounters with Shoto Todoroki during the U.A. Sports Festival. He was able to focus One For All into his hand to break Shoto's defense during the Cavalry Battle, and also to punch him a few times during their match in the finals. At that point, All Might believed that Izuku was capable of harnessing only five percent of One For All's power without backlash. Izuku's fight with Shoto proved he was okay with injuring himself as long as he believed he could be healed later on by Recovery Girl. After the conclusion battle, Recovery Girl made it clear that she now refused to heal self-inflicted injuries of that nature, demanding Izuku find a new way to utilize his Quirk.

It is only after training with Gran Torino that Izuku discovers a way to use One For All with no repercussions. During their time together, Gran Torino taught Izuku that his movements and smashes were too slow, as he treated One For All more like a special move than a natural ability. While training himself in an alleyway, Izuku tried regulating his Quirk's power into his legs in order to scale the side of a building. Unfortunately, he discovered that Gran Torino's previous evaluation was correct and failed to do so.

Izuku eventually realized that he was using One For All solely in the limbs that required it, thus severely slowing down his overall reaction time. To compensate, Izuku developed One For All: Full Cowl, which takes advantage of the five percent Izuku can safely work with to increase his strength and agility by letting this small amount of One For All to flow throughout his whole body.

Using Full Cowl, Izuku can easily scale the side of buildings, jump large clearings between structures and quickly navigate through cluttered areas. Many of his newfound movements are attributed to watching the way Katsuki Bakugo propels himself using his Explosion Quirk. Izuku could spar close to the speed of Gran Torino and even held his own against Stain in his first real fight. Even so, if Izuku does not remain calm and alert while using his Quirk, he might go over his five percent limit and injure himself.

During the rescue training race, Izuku used his Full Cowl to enhance his speed and agility and was able to outpace his classmates. This display garnered much shock from his classmates and All Might.

In his second fight with Katsuki, Izuku instinctively found out how to wield One For All at eight percent of its full power without repercussions. Izuku can access any percentage of the full power of One For All, however, any higher than his current limit will damage his body as seen in his fight with Overhaul.

While in physical contact with Eri, Izuku was temporarily able to use One For All at 100 percent of its full power with no consequences, due to Eri's Quirk constantly rewinding all of the damage Izuku was doing to his own body.

In his training sessions with All Might around the time of U.A.'s Cultural Festival, Izuku revealed to All Might that he had discovered during the internships he could use 20 percent of One For All for a very short time if in a desperate situation. Any longer than a brief instant would result in harm to his body. Lamenting his "inability" to perform any long-ranged moves in the battle against Overhaul, Izuku was told that he already had the capacity to do so. All Might had planned to wait until his disciple had control of at least 15 percent of One for All to begin teaching him said moves, but seeing that Izuku had learned how to briefly bring out 20 percent of One For All, which was more than enough to manipulate wind pressure, All Might decided to instruct him on how to perform them. After learning the new technique and receiving new equipment from Hatsume to help harness the wind created, Izuku was able to put the super move to the test in his battle against Gentle Criminal.

During the fifth round of the joint training session between Class 1-A and 1-B, dark energy starts to shoot from Izuku's arm that heavily damages his surroundings, and pulls him along against his will. This causes him intense pain and he can't deactivate One For All in this state. With the efforts of Uraraka and Shinso, they were able to stop the rampage of One for All by brainwashing Izuku, but this sent Izuku's mind into his subconscious where he meets a preceding wielder of One For All. The man that explains that the quirk factors of previous holders have merged with the core of One For All and there are six other quirks that Izuku will manifest and that the quirk that he had when he was alive is called Black Whip. The man also tells Izuku that all of the quirks have been strengthened since the eras of the original holders of the quirks since One For All stockpiles power.

Quirks within One For All
One For All is a Quirk that has merged the Quirk factors of each previous user within the core of One For All and increases their Quirk's power. Izuku is the first user capable of using them.
 * Unnamed Quirk Transferring Quirk: a Quirk belonging to the younger brother of All For One. This quirk allows the user to pass on their Quirk to others. After it fused with the stockpiling Quirk given to him by All For One, it created One For All. It also merges the Quirk factors of later users of One For All within it when passed on.
 * Unnamed Power Stockpiling Quirk: The Quirk All For One gave to his brother, this Quirk stockpiles power and increases in strength over time. It gives the user immense super strength and is the primary ability of One for All. After it fused with the unnamed transferring Quirk possessed by All For One's younger brother, it also increases the power of the Quirks used by the later users of One For All.
 * Black Whip: A Quirk wielded by an previous unnamed user of One For All. This Quirk allows the user to fire dark energy at opponents at long ranges. The dark energy is also able to attach to the surrounding and pull the user around. It is currently used by Izuku Midoriya.
 * 5 Unknown Quirks: 5 unknown quirks that originally belonged to the previous wielders of One For All. They will eventually manifest within Izuku Midoriya.

All Might's Super Moves
Most of the attacks used by All Might are based on the names of places in America. Even the training schedule he made for Izuku was named such.
 * Texas Smash (テキサススマッシュ): All Might throws a right punch with enough force that the wind pressure sends most things flying away. This move is first used to save Izuku from the Sludge Villain.
 * Detroit Smash (デトロイトスマッシュ): All Might performs that same attack as Texas Smash except this move is with a downward punch instead of a straight punch. The punch is powerful enough to create a shock wave large and powerful enough to clear the weather. This move is first used to save Izuku and Katsuki Bakugo from the Sludge Villain.
 * Missouri Smash (ミズーリースマッシュ): All Might runs towards an enemy while keeping his hand flat and hits the enemy on the head while running past them. This move is first used against Trapezius Head Gear.
 * California Smash (カリフォルニア スマッシュ): All Might attacks with a frontal somersault leading into a downward punch. This move was first used against a villain while he was studying abroad the United States.
 * Carolina Smash (カロライナスマッシュ): All Might runs towards an enemy while keeping his hands in a cross position, then in a downwards cross chop to the enemies head. This move is first used against Tomura Shigaraki, but it is intercepted by Nomu, who withstood the full force of the attack, seemingly unharmed.
 * New Hampshire Smash (ニューハンプシャースマッシュ): All Might blasts himself towards his enemy and smashes his body into the enemy, crushing and injuring the enemy with his great weight. This move is first used to propel himself at Izuku.
 * Oklahoma Smash (オクラホマスマッシュ): All Might whirls around while enemies have latched onto him, spinning with enough force that when they are released they are easily thrown through concrete. This move is first used against Nomu however it was named during the Kamino ward incident.
 * United States of Smash (ユナイテッドステーテスオヴスマッシュ): All Might's final and strongest move. Using the last remnants of One For All left in him, All Might delivers a massive punch with enough force to reverberate shockwaves. This unstoppable attack was used to defeat All For One and marked the end of his hero career.

Izuku's Super Moves

 * Detroit Smash (デトロイトスマッシュ): The same as All Might's move, except Izuku sometimes does it in the form of an uppercut, creating an air pressure blast.
 * Delaware Smash (デラウェアスマッシュ): Izuku flicks his finger to create a powerful shock wave. Doing this fractures said finger, limiting the number of times he can use this move without gravely injuring himself to 10 times.
 * One For All: Full Cowl (ワン・フォー・オール フルカウル): This technique allows Izuku to activate 5%, and later 8% of One For All throughout his body, letting the power course and flow through him instead of concentrating it in one location, and negating the need to "turn on" the power every time he needs to use it. Activating this technique gives him enhanced strength, speed, mobility and agility. It also prevents him from breaking his bones when attacking.
 * 5% Detroit Smash (5 パーセント デトロイトスマッシュ): Izuku activates One For All: Full Cowl, then jumps into the air and delivers an enhanced downward punch to the opponent. He has also used this move in the form a straightforward punch.
 * Delaware Smash Air Force (デラウェアスマッシュエアフォース): Izuku uses his upgraded gloves to direct a blast of compressed air against his foe, possessing enough concussive force to stun Gentle while he was in mid-air, giving Izuku an opening to catch up to him. By using all five of his fingers, he can launch up to four Delaware Smashes simultaneously.
 * One For All: Full Cowl - Shoot Style (ワンフォーオールフルカウル シュートスタイル): A fighting style of using One For All that deviates from All Might. Izuku realizing that just imitating All Might's style which has its special moves centered on his fists was not the best style for him and was actually causing more harm to his arms, he developed a new style that centers more on his legs with the help of his friends. Shoot Style concentrates One for All: Full Cowl's effects in his torso and legs rather than his arms, allowing him to put out even more power due to the fact that the human leg muscles are naturally stronger than the human arm muscles, granting him more power and stability.
 * Shoot Style: St. Louis Smash (シュートスタイルセントルイススマッシュ): While using the Shoot Style, Izuku leaps into the air and before swinging around to deliver a roundhouse kick to the opponent's face. Izuku used this move to incapacitate Gentle Criminal, who had been empowered by La Brava's Lover Mode Quirk to match Izuku's use of One for All: Full Cowl at 8% of its power.
 * One For All: Full Cowl - 100% (ワン・フォー・オール フルカウル 100): Izuku activates One For All to its fullest extent throughout in Full Cowl, granting him a tremendous boost in speed and strength that allowed him to easily overwhelm the likes of Chisaki. This is first used against Kai Chisaki to protect Eri. The power increase seemingly gives him fire-like trails coming from his eyes and light colored hair. He can only use it infinitely with no damage done to his body while in physical contact with Eri because her Quirk constantly rewinds his body to a previous state.
 * One For All 20%: A technique that allows Izuku to use 20% of One For All throughout his body, it causes a lot of pain to the point that he feels as if his bones are about to break.
 * Manchester Smash: While using 20% of One For All, Izuku leaps into the air and flips forward to bring down an axe kick upon his opponent. Although Chisaki managed to dodge it, it pulverized the ground thoroughly enough that Chisaki wasn't able to completely retaliate with his Overhaul Quirk.
 * One For All 30%: A technique that allows Izuku to use 30% of One For All throughout his body. It was used in conjunction with Melissa Shield's Full Gauntlet, nullifying any normal drawbacks to using One for All at higher percentages. It is unknown how this percentage affects Izuku's body under normal conditions.
 * One For All 100%: A technique that allows Izuku to attack using the full power of One For All in one concentrated part of his body. After initial use, the limb breaks instantly. He can still use expended limbs in combat, but it causes scarring once they're completely healed.
 * 100% Detroit Smash (100 パーセント デトロイトスマッシュ): While using 100% of One For All, Izuku strikes his target with a lunging punch.
 * 1,000,000% Delaware Detroit Smash (1000000 パーセント デラウェアデトロイトスマッシュ): Izuku activates 100% of One For All during an adrenaline rush and then strikes his opponent by first using a Delaware Smash and then a powerful Detroit Smash, hence the Delaware Detroit Smash. During the climax of his battle with Muscular, Izuku manages not only to overpower but also to launch his augmented opponent with enough force to create an impact crater in solid rock with the strike alone.

Trivia

 * To date, most of the moves using One for All are named after states and cities in the USA (e.g. Missouri Smash, Delaware Smash). This is consistent with the manga artist's desire to model All Might after American comic book heroes, especially in All Might's hero form ( and ). It is unknown if, like Izuku, the naming theme is passed from teacher to student, or if this unique to All Might with Izuku's admiration carrying over.
 * According to All Might, to activate One For All, the user must clench their buttocks and scream within their heart: "SMASH!".
 * So far every named user has had a number in their name somehow correlating to what number user they are. The 7th user is Nana which is Japanese for 7. Toshinori Yagi has the kanji for 8 in his name. One of the kanji in Izuku's name can also be read as "kyu" meaning 9.
 * One For All's name is an inversion of All For One, showing the differing philosophies between their wielders. One For All showing "One Quirk for multiple people" (through passing it on) and All for One showing "All Quirks for one person". Additionally, as the "Symbol of Peace," Toshinori has used his quirk for the defense of all.
 * It is unknown if One For All can be passed back to a previous user if the current user allows it.
 * As the truth behind One for All is only known to a select few, Izuku's Quirk is listed as "Super-Power" in U.A. and other records.
 * Toshinori still has a few side effects left over from One for All such as; if he attempts to activate his (former) Quirk he still goes in muscle form for a short period of time although his super strength is gone for good.
 * According to Gran Torino and Toshinori using One for All at 100% took far less time for Toshinori than most users and even Izuku.
 * Izuku states that One for All is "one of the seven great mysteries of the world". The other six "great mysteries" are unknown.
 * Other than Toshinori and Izuku, all six of the successors of the quirk had an original quirk of their own prior to inheriting One For All.

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