The story begins with a teenaged boy named Kou who came to the slums to search for Takumi, his missing big brother who ran away years ago. The brothers reunite, and it turns out that Takumi now heads the Mikuni Detective Agency. Kou wants to bring Takumi back, but he doesn't want go back home himself. So, he starts working at the agency, doing odds and ends.

(Source: Anime News Network)