He is Asago's father and the kumicho of the Silver Dragon Clan Sumongumi, the largest group under Kuryugumi. He is strict with her and always pressures her to be the best at everything, emphasizing that her duty as a seisai comes before anything else. After Rui severs Asago's right arm, Sumon forbids her to seek psychological help to ease the pain of adjusting to the new prosthetic arm, so as not to appear weak. After Ryuuji is shot and rendered comatose while protecting her, Sumon also forbids Asago from returning to the Sumon house. However, some time after the engagement is canceled, Asago notes that her father permitted her to return without any sarcastic remarks, and assumes that Ryuuji must've said something to him.