Tsukasa is a living organism created by the mad scientist Rui.Rui kept Tsukasa alive and made him dependent on his master. Rui most often calls Tsukasa Tsu, but when angry he calls him by his full name, and the living organism remembers this. Tsu has the ability to regenerate his wounds when he sleeps, but he has a very weak immune system and gets sick often.He is completely dependent on Rui and loves him, even though fear is at the root of their relationship. Rui forbids Tsukasa many things