Tantei to Neko-chan

An ex-police detective turned private investigator x an incomprehensible young man. Kawasaki runs a detective agency and by the time he realizes it, Okachimachi, who is sometimes an uninvited helper (?) and sometimes a target of investigation himself (?!), has crept his way into his heart! (Source: Gentosha Comics, translated) Note: Includes an extra chapter.