Ari-sa, who has been married for a year, is still having sex with her husband every day and they are very much in love. However, her husband suddenly decides to go on a one-month business trip. Her husband thinks he will be lonely, so he arranges for his sister to live with Ari-sa during the trip. However, in reality, his sister Sumire is bisexual and has been watching her younger sister Arisa since she started dating her brother, waiting for the right moment to pull her into the lesbian world.
