Itsuka Tenma no Kuro Usagi Portable

1st year high school student Kurogane Taito is a disillusioned youth. He has thrown away the belief that hard work and effort will be compensated. Now, he simply exists as the days pass him by.

However, there is something that he has forgotten. A stolen memory of a girl, a pact, and a curse. 9 years ago, the young Taito had met Saito Himea, the eldest vampire, and made a pact with her.

Now, Taito's memories are about to be restored, and he will remember the girl which has been kidnapped and kept imprisoned for the past 9 years, waiting for him to free her.

[from AniDB]