Sen Owari has just become a convicted killer. An exchange student studying at Columbia University, Sen had entered into an illicit affair with one of his female professors. After murdering his lover's husband, he is sentenced to 80 years for first-degree murder and is locked away in a maximum-security US prison built entirely underground—UGH. It is known to the inmates as the Under Grand Hotel, and the majority of them will spend the rest of their lives here. Sen's status as the only Japanese person incarcerated in the facility has left him an outcast and target. Attempting to navigate a world he cannot possibly hope to understand, he is determined to win the protection of the prison's "shutcall"—the murderous drug dealer Swordfish. In return for the promise of safety, Sen will hand over his life and body. [Written by MAL Rewrite]