Shiro

Shiro wears a white cloak made from anti-Teacher fibers and a white mask covering his face and voice.

When his face is shown, Shiro has wavy black hair, sharp fox-like eyes, and a mechanical left eye due to an old injury.

He is a 34-year-old man.

After revealing his identity, he ditches the voice changer and mask, showing his real face.

Shiro acts calm and gentle at first, especially to people he just met.

His true nature is arrogant, cruel, and egoistical.

He treats everyone as disposable tools for his own plans.

If someone is no longer useful, even someone he picked up like Itona Horibe, he abandons them without hesitation.

He can betray his allies and sacrifice anyone to achieve his goals.

Even in cooperating with Kaede Kayano, he is only interested in using her as a weapon against Korosensei, not as a real partner.

Shiro's real name is Kotaro Yanagisawa.

He was born as the son of a famous biotechnology company owner.

He became the head scientist for a secret international research organization in Japan.

Shiro fell in love with Aguri Yukimura, Kaede Kayano’s older sister, after seeing her dedication, hoping her passion would rub off on him. Their relationship was mostly a political arrangement, and he treated her more like a servant than a fiancée.

He looked at her as another "test subject nobody would miss if she died."

Shiro is a genius scientist with deep knowledge of biology and technology.

He knows all of Korosensei's weaknesses and how to attack them.

He carries special hidden weapons in his cloak, such as guns with pressure light beams that cause Korosensei’s body to stiffen and tranquilizer guns.

Shiro manages to implant tentacle cells into his own body, enhancing his physical power without suffering the side effects others did.

• Korosensei: Shiro is the one who turned the human known as "Reaper" into the monster Korosensei through inhumane experiments.
• Aguri Yukimura: She was his fiancée, but more as a tool than someone he genuinely cared for.
• Kaede Kayano: He claims to be her "only brother" due to his engagement with Aguri, but Kaede sees through his real nature and dislikes him.
• Itona Horibe: He originally recruited and used Itona for his own plans, but abandoned him when he felt Itona was no longer useful.
• The Second Reaper: Shiro works with the next "Reaper" to try and kill Korosensei together.

• Shiro’s full name is Kotaro Yanagisawa.
• He is directly responsible for causing all the major events in the story, including the existence of Korosensei and the explosion of the moon.

“I see everyone else as pawns for my goals.”

“I will give Korosensei a death filled with regret and suffering.”

The Person behind the White Mask

Shiro first appears as a mysterious person claiming to be Itona Horibe’s guardian.

He wears a white costume with a mask and never reveals his real name or face at first.

The Mad Scientist

As the story progresses, it is revealed that Shiro is actually Kotaro Yanagisawa, a famous scientist and the main brain behind cruel experiments on Korosensei (originally called "Reaper").

He creates anti-matter cells, turning the Reaper into the creature Korosensei.

A Ruthless Mastermind

Shiro only cares about his own research and success.

He has no problem using people, tricking or betraying them, and even hurting them if they get in his way.

He treated both Aguri Yukimura and Kaede Kayano as tools.

When he decided Itona was not useful anymore, he abandoned him.

The Cause of the Moon Explosion

Shiro’s research and experiments with anti-matter cells end up causing a mouse experiment on the moon to explode, blasting away 70% of the moon and turning it into a crescent.

This leads directly to the dilemma of whether to kill Korosensei to prevent Earth's possible destruction.

Overwhelming Hatred Toward Korosensei

Shiro blames Korosensei for destroying his reputation and research, and seeks revenge.

He works together with the Second Reaper, using his knowledge and technology to attack Korosensei and the students.

The Final Battle

In the last assassination plan, Shiro implants tentacle cells into his own vital organs, boosting his power to near-Korosensei levels.

He attacks Korosensei and the students, showing no concern for their safety.

He forces Korosensei to defend the students, using this as a way to weaken him.

He laughs when Kaede Kayano is hurt, triggering Korosensei’s full rage.

But in the end, Korosensei’s true power defeats Shiro’s plans.

His Tragic End

Shiro is hit by the backlash of Korosensei’s energy blast and smashed into the “Shield of Earth,” which melts the tentacle cells in his body.

All of his limbs are severely damaged, and his vital organs are ruined.

He survives, but is left completely paralyzed and bedridden, needing machines and constant care to even stay alive.

His research is declared useless and a failure.

He is forced to live out his life dependent on others, unable to even die by his own will.

• In the live-action movie, Shiro serves as the final boss, directly injecting himself with tentacle cells to become gigantic. He is destroyed in an instant by Korosensei’s energy beam.
• The actor who played Shiro in the movie, Narimiya, described him as "a sad character whose intelligence led him on the wrong path."
• Shiro is seen as the origin of much suffering in the story, but without him, many of the main characters would never have grown or met each other in the way they did. This makes him an accidental hero in some twisted sense.