On a mission to protect peace, Hina, or Guardian Heart, is sent to Earth with strict instructions to keep her identity a secret. However, when Kazuya accidentally witnesses Hina's transformation upon her arrival, he brings her to his home. Hina believes it's okay for family to know her identity, but with magic girls appearing and revealing themselves to Kazuya, living with Guardian Hearts becomes even more complicated. As Kazuya navigates the attention and jealousy of multiple girls, his days become far from ordinary.