Tsukasa is a humanoid that at first was a small fluffy monster, but six months later became a human form. But still he can't speak properly and only says "Gururu" and "Kyuu". He became very attached to his "owner" Kamishiro Rui, which gave him the name Tsukasa. Tsukasa does not know human rules and norms, so sometimes she can do strange things. He also knows simple short words, especially the name "Rui", but still rarely speaks.