Classmates Hikari and Mizuki suddenly became step sisters after their parents remarried. Mitsuki, who is clumsy and overly obedient, is bullied in contrast to the stubborn Hoshi, who is in a group that stands out in the class. Although the two people, who have completely different standing positions and personalities, clash their true feelings that they couldn't tell anyone leak out and gradually become attracted to each other. A sister-in-law story that develops bonds by fumbling.