Fallen Angel.

Aiba Tsubasa has astounding mathematical powers. He has two younger brothers: Riku, a naive but kind-hearted university student, and Umi, who was born with a weak heart and can only be saved by an organ transplant. Their mother Takako, a gifted surgeon, abandoned Tsubasa and Riku when they were young to join a secretive medical research facility that studies people with extraordinary abilities and conducts unethical experiments to create superior humans. Umi eventually receives a successful transplant, but the donor possessed an exceptional memory and could never forget anything. As a result, Umi begins to inherit the donor’s memories, gradually being taken over by the donor’s personality. When Umi escapes the facility and seeks out his brothers, Tsubasa and Riku try desperately to protect him as the organization’s agents close in.