Sukisho!(2005)

Hashiba Sora has fallen from a 4th story window and has lost all of his memories. When Fujimori Sunao comes to his school as his new room mate, Fujimori tells Hashiba that he is called Ran. Fujimori and Hashiba both have a split personality which they developed in their youth. Their split personalities, Yoru and Ran, are deeply in love. Even though it creeps Fujimori and Hashiba out what their other selves do with each other at night, they also start to fall for each other. Because of their relationship, Hashiba Sora finds out a lot of shocking facts about their youth.