Ari-sa, who had been married for a year, was still having sex with her husband every day and they were deeply in love. However, her husband suddenly decided to go on a one-month business trip. Her husband thought she would be lonely, so he arranged for his sister to live with Ari-sa during the trip. However, it turned out that her sister Sumire was bisexual and had been keeping an eye on Ari-sa since she started dating her brother, waiting for the right moment to pull her into a lesbian relationship.
