Nana Shimura/Synopsis

History
Like most people, Nana Shimura was born with a Quirk of her own, Float. During her career as a pro-Hero, she was a close friend of Pro Hero Gran Torino. At some point in her life, Nana received One For All from the sixth user, En, just before his death at the hands of All For One.

Shortly after inheriting One For All, Nana had a strange dream, where she encountered one of the previous users shrouded in dark fog telling her "It's not time yet..." Nana was mystified and decided to tell her friend Gran Torino about this strange experience.

One day, she met Toshinori Yagi, a young boy who was born Quirkless and was about to be attacked by a gang of villains. She flies in and dispatched all the villains Toshinori was about to fight with ease, floating over a group of defeated Villains. She notices Toshinori looking at her with admiration and asks the young Toshinori what he was going to do as he attempted to fight them with just a lead pipe.

After rescuing Toshinori, he explained his very ideals of the world, and wanted to create a world where everyone can smile and live happily together. For that to happen, the world needed a "Symbol of Peace" to inspire a new age of harmony. Toshinori believed he could become the pillar that inspires people everywhere. At first, Nana had second thoughts since Toshinori was Quirkless, but she liked Toshinori and his strong sense of justice. She decided to take Toshinori as her student and became his mentor. Entrusting him with One For All, Nana took it upon herself to train All Might and she was assisted by Gran Torino.

During her lifetime, Nana married and had a son, Kotaro Shimura, with whom she had an excellent relationship. At some point, her husband was killed by a villain. To spare her son from the same fate, Nana left her son in the care of a foster family, telling Gran Torino and Toshinori to never come into contact with him under any circumstance.

To protect Kotaro from All for One, Nana even had to cut off anything connecting her to her son, to the point she even doctored the family register, so Kotaro can't be tracked back to her, knowing that All For One is out there watching and waiting for the opportunity to strike. Still, separating herself from her son was a heavy emotional blow for both of them, as she was forced to declare that she "has no son". Nana left a letter to Kotaro explaining the reason for this, but Kotaro grew bitter by this abandonment, despising anything related to heroes and a certain grudge towards his mother.

Unfortunately, all this would end up backfiring very badly. His son, Tenko Shimura, would end up accidentally killing his family by manifesting his Quirk for the first time. And since both Gran Torino and Toshinori kept their promise to her, Tenko eventually became a villain under the tutelage of All For One, now rechristened under the name of Tomura Shigaraki.

Throughout Toshinori's high school years, she would continue on to train Toshinori alongside Gran Torino. During Toshinori's final year, he and the two Heroes would eventually battle against All For One. However, the villain was proven to be way too powerful for all three of them. She was wounded in the battle, and soon, Toshinori and Gran Torino were defeated by All For One

Realizing they wouldn't be able to win and how All For One was prepared to kill all three of them, Nana decides to do what is necessary and forcibly pushed Toshinori out of the way. He calls out to his master as Gran Torino swoops in and flies him away. Nana says she's leaving the rest to All Might and asks her friend to make sure his dreams come true. With her back turned, Nana points to Toshinori, signaling his time has come to take her place. Nana turns to her successor and with one last smile, reminds him that she's counting on him to save the world.

Toshinori tearfully screams for his master as Gran Torino flies away filled with grief. Knowing in her heart that All Might will rise to take her place, Nana turns to face her nemesis. The evil mastermind thanks her for entertaining him and finishes her off with a powerful explosion created from a surge of black lightning, which destroys the entire island.

At some point later, All For One got ahold of one of her hands, and gave it to her grandson Tomura to replace one of his father's hands that he accidentally destroyed.

U.A. Sports Festival Arc
During the fight between Izuku against Hitoshi in the tournament of the U.A. Sports Festival, Izuku is brainwashed by Hitoshi's Quirk, who orders him to walk out of bounds. Although Izuku tries to resist, he cannot disobey the order, but when he is about to cross the edge of the ring, Nana and the rest of the previous users appear to Izuku as shadowed mental figures. They uncloud his mind and allow Izuku to use One For All in his fingers, allowing him to escape the trance and win the fight.

Pro Hero Arc
After Izuku Midoriya falls asleep after an exhausting training session, he experiences the vestiges of One For All. Nana Shimura and the other users of One For All appear in his dream. While Izuku doesn't recognize her, he later identifies her as All Might's master. After the dream concludes, she is seen with the other predecessors blessing Izuku.

The next day, Izuku narrates his dream to All Might. All Might remembers what Nana had told him about the vestiges of One For All. She had speculated that the Quirk stores the will and memories of the previous users in order to activate its power. She had found it romantic that even after her death, all One For All users will meet each other.

My Hero Academia: Heroes: Rising
During a devastating battle between a villain with a copy of All For One's Quirk, in a last-ditch effort to defeat him, Izuku transfers One For All to Katsuki Bakugo, even at the cost of rendering himself Quirkless once more. Through the dual power of the One For All's, the two manage to take the villain down, even as the remaining embers of One For All seemingly disappear from Izuku. However, Nana and the other users of One For All, wanting Izuku to continue to harness the power, and recognizing his heroism of being willing to sacrifice his power to save everyone, only temporarily transferred the power over to Katsuki, while the full essence of One For All remains within Izuku. Toshinori tearfully thanks his master and predecessors for staying with Izuku.

Paranormal Liberation War Arc
Despite being long deceased, Nana and the Shimura family contiunes to linger on towards Tomura Shigaraki. When he voluntarily undergoes a complex and painful four-month operation carried out by Kyudai Garaki to inherit the All For One Quirk. However, the heroes storm Dr. Garaki's labs by interrupting the process with weeks left to complete, and destroying the capsule containing Tomura.

Since his heart is not beating, Tomura is considered dead. However, mentally he is in a kind of mind world, where a shadowy version of All For One appears and tells him to come to him. The memories of Tomura's dead family members appear, all desperately trying to stop him from following All For One's footsteps. The last one to appear is Nana Shimura, who grabs the back of his head and telling him to not forget them.

Tomura destroys them all without hesitation, telling them not to reject who he is. The crumbling face of Nana watches her grandson walks into his Master's darkness, embracing the path of villainy. During his fight with Tomura, Izuku manifests Nana's Quirk, Float, and uses it to contain Tomura in the sky while pulling his allies to safety using Blackwhip before he goes all out and viciously attacks Tomura with everything he's got.

The Heroes succeeds in defeating Tomura; unfortunately, during the course of the fight, the vestige of All For One manages to gain control of Tomura's body and attempts to steal One For All from Izuku, but something unexpected happens and everyone is transported into the world of vestiges. As Izuku struggles to move, he sees that All For One and Tomura are fused together, and they fight to be in control.

Suddenly Nana appears beside Izuku and tells him "they" will help him. She then speaks to All For One and expresses her disgust at seeing him again even after death. All For One is amused with Nana's appearance, taunting her as he explains to Tomura that she is his grandmother.

All For One explains to Nana as well as Izuku and Tomura the reason why the vestiges are present in the users of All For One and One For All. When finished, he "invites" Nana and Tomura to greet each other. Nana recognizes him as the child of her son, but Tomura replies that it doesn't matter. Nana somberly listens as Tomura admits that no matter how they ended up in this situation, he still hates her and begins eroding the Vestige world away.

In order to protect Izuku, Nana resists Tomura's crumbling of One For All, as All For One gloats Tomura's power born of his hatred, even when he himself is affected as well, but considers that it is still not enough when he suddenly sees that Nana is accompanied by his little brother and the first user, Yoichi Shigaraki.

Between the two of them, Nana and Yoichi start to reject Tomura's power, so All For One decides to use his in combination with Tomura's to seize One For All. The villain derides Izuku, claiming to his brother he made a mistake in selecting him. Yoichi refutes his big brother's words, telling him that Izuku is the most suitable heir for his Quirk, and together with Nana they reject All For One, resulting in Izuku and Tomura falling away from each other in the real world, knocking both of them out and stopping Tomura from stealing One For All.

In the aftermath of the battle, while Izuku is in a comatose state, Nana and the other predecessors speak to him about the true nature of One For All. After this discussion, she approaches him and asks if he can kill her grandson, Tomura. She clarifies that it isn't a request, but a question of his resolve. Because of One For All, she reminds him that they were able to telepathically sense his emotions, and they could also sense that he saw him as someone who needed saving. The users all agreed that one must have an incredibly strong will and overbearing emotions in order to override the basic principle of One For All, which means All For One is using Tomura's hatred to complete the job.

Nana confronts Izuku, confirming to him that Tomura is her grandson, and that the reason he became this way is because she left his father at a young age to fight All For One, feeling all this is her fault. She knows how unfair it is to force this burden onto a young boy, but reminds him that if ‘that thing' ever reaches its potential and becomes the ultimate evil, no one will be able to stop him. She says that it won't be enough to forgive and understand him because some people cannot be saved, and that if Tomura is one of them, a person who looks like they need saving but can't, does he have the resolve to stop him at all cost?

After a moment of silence, Izuku says he knows that countless people died and many of his precious friends were hurt because of Tomura, but he stands his ground believing that One For All is a Quirk meant to save lives, not kill; that All Might taught him that, and that he and all the other users who have helped grow and cultivate the power, have in the process saved and brought hope to countless people. He accepts the real possibility that Tomura can only be stopped by killing him, and he doesn't know how he will deal with everything exactly yet, but he still wants to try and save "that little boy", all the while briefly transforming into his child self.

Moved into tears, Nana cries in hopeful of Izuku as the first user comforts Nana. She apologizes for testing him like this, telling him to give her best to Gran Torino when he wakes up, admitting that while they made the wrong choice, their successors are determined to make things right.

Dark Hero Arc
In the aftermath of the Paranormal Liberation War, All For One has escaped from Tartarus, and proceeded to break into several more maximum security prisons, liberating the inmates. Due to the chaos inflicted by Gigantomachia and the mass breakout of prisoners, the whole country entered a state of total chaos and anarchy. In addition, many heroes resigned and called it quits because of the massive criticism of their work, and the destruction spreading unchecked.

Izuku was forced to leave behind U.A. and his friends so he can focus on finding the villains. With all the users on his side backing him up, Deku prepares to head out.

However, when Izuku is starting to tire out after days of fighting villains nonstop, Nana and the other inheritors of One For All try to convince him to rest before Danger Sense warns him of another threat and heads off, ignoring their words. In the vestige world, Nana fears that her emotions are getting the better of Izuku, while the other inheritors assure her that by going over his limit, he's acting like a true hero would do. It was all through his former classmates that Izuku was finally able to rest easy knowing that they still got his back.

Final War Arc
As the final battle between the heroes and villains commence in the Final War, Izuku prepares for his final encounter with Tomura. While a snag in the plan delays his arrival, he eventually makes his way over to the U.A. Flying Fortress designed to contain Tomura to fight him. After regaining his bearings, Izuku confronts Tomura, who over the course of the battle has transformed himself into a hulking beast covered in fingers, and addresses him as "All For One", asking if Tomura is still within him.

"Tomura" claims that he no longer exists, as he and All For One's psyches have melded together into a perfect new being. However, Mirio Togata reveals that during their battle, the villain reacted to one of his taunts like that of a child, believing them not to be as melded as he thinks. The spirit of Nana looks towards Tomura's left hand, which is comprised of the faces of the deceased Shimura family, including that of her son, Kotaro. Seeing him look at her, she tells Izuku that he is still in there, sparking the battle to resume.

Izuku activates the Quirk of the Second User, Gearshift, and now with all the Quirks unlocked, unleashes the full power of One For All upon Tomura, overpowering him, with Nana and the other predecessors right there behind him. After Izuku destroyed Tomura's Absolute Defense Form, Tomura releases the pent-up damage in a explosion which weakens All For One's influence over him, allowing Tomura to regain control of his body. Izuku drags Tomura out of the U.A. Flying Sky Fortress to bring their war down on the ground and fight to the death once again.

Nana's influence on Toshinori continues on to push him to fight All For One who was on the verge of Warping to Tomura's location in his new exosuit, the Armored All Might while the villain is rewinding into his younger prime state.