Ushiro - Fukigen na Shinigami.

"In exchange for your life, I'll grant you one wish."

Ushiro spends his days looking for people desperate enough to die so he can approach them to convince them to die, so he can eat their souls. Despite how it seems though, he is not completely heartless, offering to grant the people a single wish to come true in exchange for it. However, much to Ushiro's dismay, an upbeat high school girl can actually see him, and on top of that she goes out of her way to convince people not to die.

Being drawn together through some kind of string of fate, the two go on to meet several different people who are struggling with hurtful pasts, perverted presents and foul futures, both doing what they can to help.