"I never thought I, a normal housewife, would end up in this kind of relationship with my brother at this age..." Aya Kurahashi (Yea Ai), an older sister in her late 30s with two children, takes on the task of doing housework for her younger brother Takumi, a bachelor in his 30s, to help with the family finances. However, Takumi, who has developed a fetish for mature women, has secretly developed a desire for Aya... After a drunken relationship, Takumi continues to pursue her and proposes a casual relationship. Although he says it's for the sake of the family finances, Aya's body is drowning in guilty pleasure as she experiences her first adulterous experience...