Hanatsukihime, Virgin Blood: Hiiro no Bansan Recommendations
It's the same story about a demon/vampire raising a young girl for only a short amount of time.
[spoiler]And then he falls in love with her which would have to let him choose who is to die - he or her?[/spoiler]
!This spoiler contains both story's ends!
[spoiler]And even though only one was supposed to be able to keep on living, in the end they both survive in both stories.[/spoiler]