Makai Senki Disgaea 4

Valvatorez is a vampire who's sworn off drinking blood due to a promise he'd made in the past. The once great Tyrant is now a Prinny instructor in charge of reforming Prinnies into obeying their orders as instructed, who takes great pride in his work.

Fuka Kazamatsuri is a girl from Earth who's died and is sent to hell as a Prinny in order to atone for her sins. However, instead of being completely turned into a Prinny, she kept her original appearance and was only given a Prinny hat and jacket. She believes everything happening around her is all just a part of a dream she's having.

This is what started the adventures and encounters that lead Valvatorez into trying to show Fuka the reality before her and revealing the importance of the promise he made many years ago.