Asamura Yuuta never expected to gain a stepsister when his father remarries—especially not Ayase Saki, the school's most renowned beauty. Drawing lessons from their parents' failed relationships, the two agree to maintain careful emotional distance. But living together proves more complicated than planned: Saki, who sacrificed everything supporting her family, struggles to rely on others, while Yuta finds himself uncertain how to connect with this unfamiliar family member. Sharing the same roof, they gradually discover the unexpected comfort of genuine cohabitation. With each passing day, the awkward distance between strangers shrinks. What begins as a practical arrangement slowly transforms into something deeper—a bond that could kindle into affection and perhaps even love.