Hina, also known as Guardian Heart, is dispatched to Earth on a mission to safeguard peace... under strict orders to keep her identity secret. Consequently, when Kazuya accidentally witnesses Hina transforming upon her arrival on Earth, he is compelled to take her in. After all, it is acceptable to know a secret identity if you are family, correct? That is at least what Hina believes! However, as if residing with Guardian Hearts were not troublesome enough, magic girls now appear to be showing up everywhere and revealing themselves to Kazuya! Can Kazuya withstand the attentions—and jealousies—of so many girls? One thing is certain: Kazuya's days will be anything but dull!