Otosaka Yuu starts off as an arrogant cheater who wants others to admire him. He isn’t content with just being good-looking. He aims for the position of the smartest student of his grade and when it comes to girls, only the school madonna is good enough for him. He puts great effort into his preparations, abuses his supernatural ability to cheat his way through life, and even frivolously puts other people in danger for the sake of his schemes. He doesn’t care much about other people.
His shenanigans end when he gets subjugated by Tomori Nao. She knows his true nature, she’s smarter, driven, and always one step ahead of Yuu. Others in his position might have tried to break free from Nao’s control, but Yuu gives up rather quickly. He is weak. He lacks courage, determination, and a decent reason to oppose her. “I don’t want to” and “It hurts” aren’t good enough a reason.
Yuu is by no means hero material.
He gets forced into the position of a Hero’s sidekick.
As he reluctantly follows Nao around, helping her save people he doesn’t care about, he starts getting used to his new situation and gets a little bit closer to his new colleagues, Nao included. He’s not exactly the obedient type, but he ends up doing as he’s told anyway. His “ambitious jerk” personality only awakens when it comes to him or his precious little sister Ayumi. He has no qualms throwing his colleague Joujirou out of the window just to make sure he doesn’t ruin Ayumi’s meeting with her favorite idol.
And yet he fails to save Ayumi. Grief-stricken, he runs away, taking out his agony on delinquents on the streets as he once again finds joy in dominating others - this time through violence. Despite “going wild” like this, Yuu doesn’t lose control completely. He doesn’t kill anyone, nor does he leave his opponents with lifelong injuries.
Yuu is not villain material, either.
Admittedly, he is a skilled fighter.
It is once again Nao who stops him from straying from the right path and helps him recover. As Yuu begins to come to terms with the tragedy, he loses some of his selfishness and develops a more understanding, a more caring side, going out of his way to help other people (in this case Nao’s brother) of his own accord for the first time.
Through a chain of events, Yuu’s position changes.
He finds out that he is the strongest ability user out there. He goes back in time and saves Ayumi. He regains memories from an alternative timeline and finds out that the world he lives in is far more cruel to ability users such as himself than he ever imagined. As if to drive this point home, Yuu is soon targeted by a foreign group of criminals. They kidnap Nao, who had done so much for him, to lure him out.
This is where Yuu is supposed to step up as a hero, but he still lacks the inner strength. Remember, he is not hero material.
Expecting a teenager to face armed and fully prepared thugs to save two lives is a tall order and Yuu almost breaks down when he is demanded to do just that. But he can’t simply abandon Nao and eventually, he works up enough courage and determination to go save her after all.
However, he fails, as do his enemies. Nao survives the confrontation only thanks to Kumagami’s sacrifice. Yuu loses time leap.
This is where Yuu grows the most as a person. He realizes his feelings for Nao and boldly confesses. He realizes what it is he wishes for: to make sure the people he loves won’t have to suffer. He overcomes his failures, decides to take things in his own hands and accepts the sheer impossible task of singlehandedly saving all ability users in the world, in order to end the conflict for good. Thanks to his friends, he also learns what it truly means to take away someone’s ability.
He never lacked power or fighting prowess. But only now did he develop inner strength, courage and determination, for now he has something he wants to protect. Only now did he become capable of taking on the world.
Yuu was never meant to be a hero. He never wanted to be one. Yet he decided to become one on his own.
So his battle begins. He struggles, he stumbles, he gets weary, he comes close to losing heart. But he perseveres, even as he is losing himself and forgetting what it is he is fighting for.
And he succeeds.