Miri Unasaka, 4, travels to Tokyo all by herself on Christmas Eve in search of her father. Miri is led to a large hotel and a man carrying what appears to be a delectable cake by the brilliant lights and festive ambiance. The youngster, however, has just unwittingly become the focal point of a complex, failsafe scheme for killing a violent mafia boss.
Kazuki Kurusu and Rei Suwa are professional killers who live together in order to escape their dark childhood experiences and be emotionally detached. There is only one logical course of action when their plan goes awry and they find themselves taking Miri home: give Miri back to her mother. But Kazuki, who secretly adores playing a parent, is swiftly won over by the child’s beautiful laugh and pure worldview, and soon Miri finds a place in Rei’s impenetrable heart.
The unexpected nature of Miri’s every action makes rearing a young child more difficult for Kazuki and Rei than any of their assignments. Despite the significant risk to their careers, Kazuki and Rei—both adopting the endearing moniker “papa”—decide to give Miri a typical upbringing despite the overwhelming odds against them.
