Oboro Shirakumo/Synopsis

History
During Oboro's first year at U.A. High School he meets Shota Aizawa and Hizashi Yamada where they all become best friends.

During his second year on a rainy day, Oboro found a cat that Shota Aizawa left an umbrella over. He took the cat and the umbrella with him to class, where he arrived through the homeroom class window using a cloud he created with his Quirk. His teacher, angered, told him off for not using the door like everyone else.

Soaked from the rain, Oboro interrupted roll call to ask if anyone had a towel, although it was to no avail. He also asked Shota if he dropped his umbrella and, when he affirmed, handed it back to him.

Since his clothes were wet, Oboro decided to change into his gym attire in front of everyone. This caused commotion among his classmates, so he used a cloud to censor himself. Oboro pulled out the cat he rescued earlier from the rain, which was met with adoration from his classmates. He allowed roll to continue after getting dressed, and placed the cat on a cloud pillow.

Class 2-A's homeroom teacher began by reminding students that most second-years did work studies during summer vacation to get a taste of what the world of a Pro Hero was like. Oboro, Shota and Hizashi were reminded they have yet to pick an agency to sign up for.

Oboro and the rest of his class geared up for Joint Exercises with Class 2-B that consisted of Battle Training, Rescue Training, and Entertainment Lessons. He excelled in each exercise.

A few days later, Oboro's teachers discussed his chance of landing an agency. His homeroom teacher said he didn't have the grades, but made up for it with a positive attitude and, wherever he did go, he would manage at his own pace.

After school, Oboro, eating sushi, joined Hizashi, Shota and the cat he rescued on the school rooftop. The trio discussed the practical usages of Shota's Quirk, and Hizashi suggested he should go the battler route so he could fight Villains on even terms, and Oboro commented that Quirk matchups can make or break a fight. Shota replied that he wasn't much of a fighter and that he didn't know what would he do against heavy brawlers. He started to explain his reasoning but was distracted by Oboro, who was trying to feed the cat his sushi. Shota told Oboro not to give him human feed, and gave his friend some school milk for the cat instead. Shota reminded him that animals aren't allowed at school, but Oboro just responded that he'd feel worse if he left the cat at home all day.

They were then interrupted when third year Nemuri Kayama, clad in her hero costume, spotted them having lunch on the rooftop, admiring their "youth" for their breaking of the rules. Oboro asked why she was there, and she explained that she'd just finished at her Work Study for the day and needed to do some paperwork at school before going home. Nemuri said that the roof was one of her favorite places, and Oboro was happy to learn she was also a rule-breaker like them. The trio noticed Nemuri's revealing attire, and Shota asked her if there was more to hero costume, jokingly wondering if it was made up of some high-tech material that was invisible to idiots. Oboro, oblivious to the joke, excitedly said that he is happy to be an "idiot." Nemuri explained the functions of her costume, leaving Oboro to admire her beauty.

After her explanation, Nemuri spotted the cat Shota is holding. Oboro explained that he and Shota were going to take care of it, but Nemuri exclaimed that they really shouldn't have animals at school, swiping the cat away. She asked the boys the cat's name, but they said they didn't yet have one for him. Pondering this, the third year asked each of them their favorite food, to which Oboro replied "sushi," and so Nemuri decided that would be his name. Oboro then hopefully told her they need to find a home for him, but Nemuri tells the them she can't take Sushi in because she's expecting to move after graduation, but also because it's harder to get married as a single cat owner. Nemuri said she'll have him temporally until the trio find him a proper home, but Oboro laughed and said that Nemuri would probably end up getting attached and keeping him for good.

The next day, Shota and Oboro hung out on the roof again. Oboro said that handing off Sushi was the most responsible thing they could've done, and Shota agreed that he'd be in safe hands with Nemuri. Oboro went onto say they weren't in any condition to take care of him themselves, and then began talking about Work-Studies. Hizashi had been assigned a battle-oriented one already, leaving them the last two without one.

Nemuri suddenly came up from the rooftop door and spotted the two, walking over to them. They thanked her for taking care of Sushi, and she showed them a clip of him she'd taken that morning. Disturbed by Sushi's bathroom video, they then asked her about her Work Study and if she knew someone they could study under. Nemuri stated she knew the perfect place for little ones with nowhere to go, and told them that her boss would take anyone, inviting the two of them to join her.

Oboro and Shota accepted her offer and begin their Work-Studies with His Purple Highness. One day, out in the field, a robbery was happening when Oboro and Nemuri entered the scene. Nemuri shouted that Purple Revolution Agency had arrived, and the Robber Villain panicked and used his Smoke Quirk to attempt a getaway. While the smoke was spreading, the Villain started to escape and Oboro began to chase after him. Nemuri stopped him and said the smoke could be toxic and that the two of them should prioritize evacuating the citizens over chasing the Villain. Oboro yelled at Shota to stop the villain, but the smoke easily countered his Erasure. His Purple Highness then to came to his aid.

After the villain escaped, His Purple Highness gave the trio some feedback. Oboro was praised for his quick reaction without hesitation and good judgement; he might've been inexperienced, but would grow from this. However, His Purple Highness criticized Shota, not for arresting the villain, but for his gloomy face. His Purple Highness advised him to smile more to transmit confidence and hope to folks in trouble.

Later that evening, Oboro and Shota were in the locker room. Shota was thinking about His Purple Highness' advice, but he was gloomy over letting the Villain escape. Oboro reassured him, saying he should just to keep smiling even if he screwed up. Shota received texts from Nemuri of Sushi, which made him smile, and Oboro happily pointed out his grin.

Oboro, now partly dressed, asked Shota what would he do against the Villain if he ever encountered him again. Shota was slumped and didn't know what he could do because the smoke would irritate his eyes if he got close, and if he was too far away he couldn't use his Quirk. Oboro knew that it was a bad matchup even for him, so he said he could lend his goggles to Shota so his friend could can get close to the Villain without smoke getting in his eyes.

A few days later, while patrolling, Shota spotted the same Villain again. Thanks to Oboro's goggles, Shota was able to advance closer than last time and temporally erase the Villain's Quirk. The Villain angrily attacked Shota, but was caught off guard when Oboro suddenly jumped from his cloud, managing to subdue the Villain with his quarterstaff. Oboro and Shota successfully immobilized the Villain and were victorious. His Purple Highness congratulated them both on their teamwork, and Oboro and Shota both smiled triumphantly while the bystanders praised them for their work.

A new semester begins, and it's explained that Class 2-A and 2-B would be having Two on Two Battle Training together. Hizashi noticed Shota had added Oboro's signature googles to his hero costume. Oboro happily told Hizashi that they were marketing themselves as a duo, but Shota just said the goggles were for the sake of protecting his eyes so he could use his Quirk more easily. Sensoji interrupted the conversation, saying that they stole his eye protecting idea. Oboro laughed it off.

The Battle Training teams were being selected when Oboro suggested that, since Shota and him were doing their Work-Studies together, they could team up. The Class 2-A homeroom teachers agreed and paired them up, leaving Hizashi and Sensoji to be paired up against them well. Before the two duos started their fight against each other, Sensoji demanded that Shota hand his googles over if they lost. Oboro accepted and wagered their googles against Hizashi and Sensoji's shades. Oboro told Shota the goggles symbolized their friendship and that they have to defend them together.

The matchup began, and Sensoji rushed in with a Blast attack against Oboro and Shota. Shoto and Oboro dodged, and Oboro countered using his Super Move, Cloud Cover, to temporally cloud his opponent's view. Oboro's clouds surrounded the battlefield, so Sensoji prepared to blast them away. However, Shota came up from behind him and erased his Quirk. With no way for Sensoji defend himself, Oboro landed the final blow on him with his quarterstaff. Oboro and Shota were victorious. The wager was called off by Shota, causing Sensoji to storm off. The Class 2-A teacher said to Oboro and Shota that their Quirks worked well together, telling them to keep up the good work.

Later, Oboro was hanging out with Shota when Hizashi showcased his new googles to match the other two. Oboro happily said that they could sell themselves as a trio. Shota thought he meant that Hizashi was coming to Purple Revolution Agency, but Oboro corrected him, saying that he was talking about the future when the three of them could start their own agency. Hizashi and Oboro would start the combat and Shota would be the edge in battle to allow them the final blow. Nemuri showed up and admired the youths bantering. Oboro then offered to add her into the agency, but Nemuri declined and stated she'd rather be independent with young men waiting on her. Oboro stated he wouldn't mind waiting on her and would later give her a pair of googles to match the trio.

A week later, Oboro was patrolling Tasomiya Ward with Shota. Oboro created a cloud to lend a ride for a group of nursery kids. Shota guided them and made sure the group looked both ways before crossing the street. Oboro commented that he's a natural with kids and suggested that he should work at a day care or be a school teacher, but Shota cringed and disagreed. The duo and kids said their goodbyes.

Oboro said Shota was observant but also that he had a tendency to overthink. Oboro believed that Shota needed to stop psyching himself out and that he could do anything if he just put his mind to it. Shota didn't believe he's good enough to work at a day care or be a teacher.

The conversation was interrupted when Nemuri gave an order to start evacuating the area because a powerful Villain was causing havoc. The duo ran back to the kids, and Oboro again creates a cloud, this time to guide them to safety. The Villain, Garvey, came into their view, causing them to panic. His Purple Highness came in to buy them some time so that they could focus on helping the kids. Due to Garvey's Quirk, he released Hizashi's Voice and Sensoji's Blast onto the city, causing mass destruction. Rubble came loose above the kids, and Oboro quickly created a cloud above them to shield them. Due to him protecting the kids, Oboro was left defenseless and was crushed by the rubble. Shota screamed for Oboro, but no response came and the kids started to sob.

Shota faced Garvey head on, hearing Oboro's voice guiding him. Shota successfully defeated the Villain, and proudly yelled out "I did it!" Shota was being praised for his action when he interjected and say it was a team effort with his partner, Oboro, cheering him on. Shota asked Nemuri how Oboro's wounds were looking but she didn't answer him. Assuming the worst, Shota told her that he should be taken to the hospital immediately.

Nearby, Hizashi and Sensoji spotted Oboro's speaker and picked it up. They noticed it was broken, but Shota said that can't be true. Shota told them that Oboro's voice was cheering him on the entire time, but Sensoji told him it was likely he was giving himself a pep talk and imagining it was Oboro. Shota brushed off Sensoji's comment, believing that it was his friend's actual voice. Shota approached the rubble where Oboro was knocked out, and saw Oboro's body bag covered in blood.

After his body was removed from the area, Nemuri told Shota and Hizashi that they should get inside. Hizashi told her the rain fitted the mood that they're in and that she needn't worry about them. Shota remembered all his memories with Oboro, and, with Hizashi by his side, they mourned the loss of their friend.

After his death, however, All For One stole Oboro's body before it was cremated. He subjected his corpse to several experiments until he somehow resurrected him as the Nomu Kurogiri. Kurogiri behaves differently from Oboro; and though he retains some aspects of his former personality, he does not remember anything in his life as Oboro Shirakumo. Instead, he was conditioned to assist and protect Tomura Shigaraki.

Joint Training Arc
After the U.A. faculty conference, where Hitoshi Shinso was officially admitted to the Hero Course, Hizashi brings Oboro up to Shota as they are walking down the hallway.

Paranormal Liberation War Arc
Bioengineered into Kurogiri, he was working for the League of Villains and took care of Tomura Shigaraki for years, until he was finally arrested and sent to Tartarus. Once there, he was questioned, but he did not leak even the slightest detail about the League of Villains or Tomura.

In the absence of progress, the detective Naomasa Tsukauchi and Gran Torino decide to analyze him. From the DNA extracted from him, they discover important details about Kurogiri: First, he is like a Nomu, and he is "programmed" to not be able to say any important information about the League or its members. Second, and most important, Oboro's corpse was used to create Kurogiri, and Kurogiri's Warp Gate Quirk is artificial and was created by a fusion of multiple Quirks, including Oboro's Cloud Quirk.

With this information, they call Shota Aizawa and Hizashi Yamada, who were Oboro's best friends when they were students at the U.A. Once they arrive at Tartarus, Naomasa and Gran Torino explain them about the situation. Since the Nomu with conscience retain the traits of their previous personality, despite their memories have been altered, and they hope that with their help they can "bring" Oboro back.

Shota and Hizashi are left alone with Kurogiri in the interrogation room, and after ascertaining that Kurogiri is Oboro, since he shows the same personality trait of caring for others, Shota start to call for Oboro Shirakumo. Kurogiri is confused, saying that he is mistaking him for another person, but Shota continues to reach out to Kurogiri, showing him his goggles and cries out to Oboro, with tears in his eyes, saying if he is still in there somewhere, then the three of them will become heroes together.

Shota's prayers take effect in Kurogiri and managed to get Oboro to briefly resurface and break though the black mist enough to confirm his identity. As Oboro tried to fight off Kurogiri, he just managed to hint at a hospital before Kurogiri fell unconscious.