夜行 妃古壱

Yakou Hikoichi is a character in the manga, Usogui. He is Referee #2 of Club Kakerou. Along with Nowa Mitoshi, he is the oldest referee in Kakerou. Other than presiding over games as a referee, he is also an expert in collecting debts, and is also nicknamed "Debt Collector". He also has a twin brother, Yakou Jouichi. He is Madarame Baku's exclusive referee.

(Source: Usogui Wiki)