No. 10 of UQ Holder’s immortal squad, Numbers. Unlike the other members who achieved immortality through supernatural means, Ikkuu obtained his through science. At the age of 13 he fell into a coma for 72 years-- to keep him alive, he was turned into a cyborg. Although he is legally 85 years old, he still has the mentality of a 13 year old, and prefers to use the body of a 24 year old.
He is the son of the head of the Ameya Concern, a company that builds robots and spaceships. It can be assumed Ikkuu's family and the Concern are responsible for his robotic body, but this has yet to be confirmed.