Suddenly, two people become "siblings" after a remarriage. Hikari, the step-sister, is quiet and unpredictable. At first, the distance between them is awkward and few words, but one day, a random whisper begins to change. The sister whispers dirty words in his ear. The brother can't resist the sudden temptation. The brother loses his reason as he can't resist the temptation his sister whispers in his ear. His sister's flirtatious dirty talk slowly makes him addicted to her...