Hina, otherwise known as Guardian Heart, is sent to Earth on a mission to protect the peace... and with strict orders not to let anyone find out her identity. So when Kazuya accidentally sees Hina transform just when she comes 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, magic 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!