Hyakugan Maoh's son. He's a centipede youkai so he can control centipedes, but he was also skilled at Yin-Yang and used Mahjong pieces as mediums to control shikigami. He was the youkai who was the catalyst for Hakkai's transformation into a youkai, and he lost his life once at Gonou's hands. Just as he was on the brink of death he buried a Mahjong piece in his own body, turning his corpse into a shikigami. He never saw eye-to-eye with his father Hyakugan Maoh, so they weren't close. He was overcome with the need for revenge at having his entire clan, as well as himself killed, and demonstrated an almost abnormal fixation on Hakkai in his psychological attacks on the man. He's like a sinister reptile with a clingy temperament.

Incidentally, the things he had in his mouth like a cigarette are Mahjong counters. They can also be thrown like needles. The name Chin Yisou was one he gave himself after becoming a shikigami. It's the name of a Mahjong combination, as well as having the meaning "to be dyed in one color".

Chin Yisou, or the single suit hand, is "All tiles in the hand are exclusively of one suit with no honor tiles". Chin Yisou controlled a huge crab-like shikigami as well, but impact-wise nothing can beat this creepy China-boy style puppet familiar. He cackles and spits seed beams from his mouth. It didn't come up in the manga, but his name is Ryuu Yisou.

(Source: KonnyakuHonyaku LJ)