It's been a long time since they last met. On the occasion of his business trip nearby, Atsushi invited his brother to his house. However, due to overtime work, Atsushi couldn't make it back, so only Mayuki was at home to welcome her brother-in-law. Mayuki shared family stories with him. Her husband is always busy with work, making Mayuki feel lonely all the time. Even her husband remembers their wedding day. Since the brother-in-law had been divorced before, he understands Mayuki's loneliness. Suddenly, there was a power outage. In the darkness, their hands accidentally touched. A kiss in a moment of recklessness led to things going beyond the final boundary. Knowing it was wrong, but just once, only in the dark... Finding an excuse for themselves, the brother-in-law hugged Mayuki, giving her one unforgettable night...