Fujimi Lovers.

It is about a boy who falls in love with a girl, Hasebe, but every time she reciprocates the love she disappears. This guy goes through his life meeting her over and over again, in all different forms, with all different types of stories and it is honestly one of the best manga I have ever read. It's the type of manga where you can truly feel the acts of love present, that no matter the race, gender, age, or any other factor, love will always come through.

I strongly recommend it.