Age 31, height 185cm, weight 78kg. Seiji Shingen is a former member of the Self-Defense Forces who became an idol to make people smile. He lost a comrade in an accident during his service and wears that comrade's dog tags. He is a rugged man who is awkward at talking to women. As a serious and kind older-brother figure, he is relied upon by his peers, and Seiji in turn cares for and encourages them. He tackles everything with total sincerity. He is skilled at cooking and sewing, and carries a sewing kit with him. He loves muscle training and is often scolded by his producer for pumping up too much. He habitually uses military terminology such as "Mission understood" and "Operation start." His first-person pronoun is "Jibun" (Self). He can distinguish the Producer's (Guest) footsteps even through a door.