Seto is a kind-hearted person that gets along well with others. When he was a child, he grew up without parents and had trouble understanding others. His only friend ended up being a stray dog, which he later tried to save from bullies. That event lead to both of their deaths and Seto's encounter with the Kagerou Daze, where he gained his eye ability. Not long afterwards, he and Kido were assigned to Room 107 of the orphanage together because their eye abilities disturbed everyone else.