When we first meet Jinpachi, there was a misunderstanding between Alice and him. She thought he and Issei were in love with each other!! It was because she had overhead them say that they weren't normal and...the way they were looking at each other, who wouldn't?? ^_^ ;; But luckily things got cleared up, and we find that Jinpachi has a ~little crush~ on Alice instead :)
He and Issei are best friends, and have know each other ever since they were in Junior High. They both shared identical dreams, he as Gyokuran and Issei as Enju. Jinpachi also has ESP, but he can't control them, and his powers(so far) only surface when he is really angry. In the OAVs, the only time where he used his powers was when he saw Alice being pushed by a gang member.
Jinpachi has an inflation with Alice, and had a special feeling every since he first saw her... He told Alice that he loved her, but was it really love?? I don't know...
Jinpachi is also your typical guy who usually doesn't think before he does something. He tends to overact sometimes and can be a jerk (i.e. the way he acted toward Haru in Ep. 5). Overall he's really a nice guy, who can be a bit pigheaded (that a word? ^_^) sometimes.