Yuu was born into the Otosaka family, where he grew up alongside his older brother, Shunsuke, and younger sister, Ayumi. His life took a dramatic turn when his brother, Shunsuke, developed the ability to travel back in time, using it repeatedly to create a world where ability users could be protected. However, this came at a great cost, as Shunsuke lost his vision due to overuse of his ability.

Unlike Shunsuke, Yuu was initially unaware of the full potential of his own powers. Believing he could only possess people for five seconds, he abused his ability to cheat on exams and manipulate situations to his advantage. However, after being exposed by Nao Tomori, the student council president of Hoshinoumi Academy, he is forced to transfer to the school and assist in locating other ability users.

As the story progresses, Yuu’s true ability is revealed he is capable of stealing the abilities of those he possesses, making him one of the most powerful ability users in existence. This realization sets him on a difficult journey, as he struggles with loss, responsibility, and the burden of immense power.

Yuu has a slim build, fair skin, and medium-length dark brown hair, which is slightly unkempt. His deep blue eyes reflect his intelligence and cunning nature early on, but as the series progresses, they also reveal his inner turmoil and emotional depth.

He typically wears the Hoshinoumi Academy uniform, consisting of a white-collared shirt, a red blazer, and dark pants. After a traumatic incident involving his sister, his appearance becomes more disheveled, reflecting his mental and emotional descent. By the end of the series, he loses his right eye, earning him the title “One-Eyed Grim Reaper.”

At the beginning of the series, Yuu is arrogant, manipulative, and self-serving, frequently using his power to cheat, avoid consequences, and gain an unfair advantage over others. He is cunning and deceptive, even faking concern for classmates to attract the admiration of girls.

However, after meeting Nao Tomori and experiencing the loss of his sister, Ayumi, Yuu undergoes significant character development. He becomes more selfless, compassionate, and determined, dedicating himself to protecting other ability users rather than exploiting them.

During a period of grief and self-destruction, Yuu isolates himself, engages in reckless behavior, and loses his sense of purpose. However, through the support of his friends, he ultimately finds renewed determination to use his power for the greater good.

By the end of the series, after stealing hundreds of abilities worldwide, Yuu loses his memories and sense of self, illustrating the high price of his power and sacrifice.

• Abusing His Power
  At the start, Yuu uses his “possession” ability to cheat on tests, impress girls, and manipulate situations to his advantage. His life changes when Nao Tomori exposes him, forcing him to transfer to Hoshinoumi Academy and assist in identifying and protecting other ability users.

• Unraveling the Truth
  Yuu soon discovers that his true ability is not mere possession but the ability to steal the powers of others. This revelation makes him a key figure in the ongoing battle between those who exploit ability users and those who wish to protect them. After experiencing personal tragedy, including the death of his sister, Ayumi, Yuu falls into despair, isolating himself and engaging in self-destructive behavior before ultimately choosing to fight for the greater good.

• Becoming the One-Eyed Grim Reaper
  In order to prevent the misuse of abilities worldwide, Yuu embarks on a global journey, stealing every ability in existence. This process takes a severe toll on his mind and body, eventually leading to his loss of memories, identity, and right eye. By the time he returns home, he has forgotten everything, including his own name and the people he once loved. Despite this tragic outcome, his sacrifice saves countless lives, making him a legendary figure known as the One-Eyed Grim Reaper.