Kimi ga Bokura wo Akuma to Yonda Koro

Yusuke Saito is a normal high school kid...well, normal enough, though there's six months missing out of his memory. But when he starts to get confronted by people who insist they're from his past, who allege that he did horrible things to them...suddenly Yusuke realizes that those missing six months may be crucial to remember. Otherwise, the skeletons in his closet may just make him a skeleton, too...
(Source: Kodansha USA)