Has been friends with Yamato since they were kids. They often met whenever Yamato came to stay with his aunt Ayano; however, Hattori would frequently get Yamato in trouble, since Hattori would take advantage of the fact that Ayano's dormitory also contained a women's bath. He is a ladies' man that, according to Yamato, prefers perverted stuff over eating. He dreams of dating all the girls in the world and the legalization of polygyny in Japan. Yasunobu is often giving relationship advice to Yamato, with rather amusing results, due to the latter's being clueless and tendency to screw up. Even though he sometimes gets Yamato in bad situations, he usually has Yamato’s best interests in mind. Much to Yamato and Miki's surprise, Yasunobu has been a straight "A" student during high school.