Thread:SecondOpinion/@comment-5758863-20150401180625/@comment-5688420-20150612001425

the problematic side of him is that he still feels guilt over the death of their father, Souichiro Kamiya, sometime before the series. that's why he became a delinquent. more of this is explained in the (purely fictional) light novel series Crisis Moon: Pact=Zer0.