Sukisho - Complete TV Series
Sora fell from the roof of his high school and was knocked unconscious.  When he finally awoke, he found a kind-hearted boy named Sunao waiting over him.  Sunao claims to be his best friend, but the fall erased some of Sora's memory.  He doesn't remember Sunao at all,  the wide-eyed young man acts like much more than just a friend.  From that day on, Sora begins to experience flashbacks in which he is not himself, but a mysterious alternate personality with hidden powers. He begins to search for the secret of his lost memory and the flashbacks, but will Sunao be his companion, or his enemy?