After they remarry, they suddenly become "brother and sister". The step-sister, Kou, is quiet and unpredictable. At first, their relationship is awkward and their words are few and far between. But one day, an unintentional whisper changed their relationship. His sister whispers obscenities in his ear. Brother can't resist this sudden temptation. He can't resist the temptation of his sister's whispered words and loses his mind. His sister's flirtatious and dirty talk is getting him hooked...