Set during Japan’s Meiji era, Firefly Wedding follows Satoko Kirigaya, a frail noblewoman whose family sees her as politically expendable because of her illness. After being targeted by Shinpei Gotō, the assassin sent to kill her, she survives by proposing a marriage with him. Viz Media, which publishes the manga in English, describes Shinpei as taking the marriage vow literally once he accepts.