Marie Takano cannot forget the single forbidden mistake she made with her stepbrother, whom she secretly loves as her first love, feeling for him more like a lover than a sibling. When her stepbrother suddenly transfers to her school, their secret, taboo relationship begins anew, hidden from everyone. "Thinking about you makes my chest ache... I love you so much... I can endure anything for you, big brother," she sincerely confesses. A gripping tale unfolds from the deep conflict between her trembling emotions and uncontrollable desires.