Yoru twin brother, since they were kids Yoku like doing the same thing as his older brother. Ever since Yoru started yoyo, Yoku began learning along with Yoru, but his skill was never a matched of and always below his brother, to a point where everyone thought Yoku was just a second-rate Yoru, which causes Yoku to grew envy and hatred, that made "Night M." to bring him into their clan.