On Christmas Day, Miri, a little girl hunting for her father, meets assassins Kazuki Kurusu and Rei Suwa. Unexpectedly, Kazuki, Rei, and Miri end up sharing a home. Follows professional assassin and best buddy Rei Suwa, who was brought up to be a contract killer, Kazuki Kurusu, a criminal contractor and coordinator. Rei is a quiet man who likes to play video games in his spare time, while Kazuki is gregarious, enjoys gambling, and loves ladies. One day, Miri Unasaka, a four-year-old girl with a mafia boss father, wanders into a hotel shootout while seeking for her father, and the two friends wind up taking care of Miri.