Bound by their parents' remarriage as children, En and Mutsuki grew up as close as siblings, spending time in each other's homes and sharing a familial bond. Over the years, Mutsuki harbored hidden feelings for En, his stepsister, emotions he could never confess. But when their parents suddenly divorce again, the delicate balance between them begins to crack. No longer quite family, yet not entirely strangers, their relationship shifts dramatically—pushing Mutsuki to finally confront En with the desires he's long suppressed.