The director of Mitsurugi Engine Shin-Yokohama's seventh laboratory branch. Soichiro is currently managing the union's protection and integrity. He is also the one who is giving direct instructions to Mei Amanohokosaka and Es. He seems to try hard to give off a cool and calm impression, but actually has a berserk side of him that he does not like to show. He admires anything cute and seems to have a say in Es' choice of clothing.