Guardian Hearts (がぁーでぃあんHearts, Guardian Hearts?) is a romantic comedy Manga, which was released in 2001. It belongs to the "harem" type of manga where one boy is romantically pursued by several girls. What is unusual for this series is that each girl has a different origin and motivation, as opposed to all being of the same or similar type.

A OVA series was released in 2003, with 3 sets of episodes. Two years later, a new OVA series was released, named "Guardian Hearts - Power Up". The first series was mainly comedic; the second series was violent and more serious but also had elements of comedy.

Source: Wikipedia