Haruka, a married woman intrigued by the online health trend of “anal sunbathing,” secretly makes a daily habit of spreading her anus in the daytime sun while her husband is away. One day, she and her husband host a party to cheer up his subordinate Sanada, who has been depressed after repeated mistakes at work. The three drink freely, and when Sanada passes out, they let him stay the night. The next morning Haruka resumes her usual anal sunbathing, only for the newly awakened Sanada to catch her in the act...