Guardian Hearts

is a Japanese romantic comedy manga, created by Sae Amatsu, which was released from July 2001 to July 2005 for 8 volumes. 2 OVA series were released respectively in 2003 and 2005.

Plot
A Guardian Heart named Hina was sent to Earth on a mission to protect the peace... and with strict orders to keep her identity secret. So when Kazuya accidentally sees Hina transform just when she descends to Earth, he is forced to take her home with him. Because it's ok to know about a secret identity if you're family, right? At least that's what Hina believes! But as if living with Guardian Hearts isn't troublesome enough, magical girls now seem to be appearing everywhere and revealing themselves to Kazuya! Can Kazuya survive the attentions—and jealousies—of so many girls? One thing is for sure, Kazuya's days will be anything but dull!