Haruka, a married woman, becomes obsessed with the internet-famous health trend "anal sunbathing" and secretly exposes her anus to sunlight every day, hiding it from her husband. One day, to cheer up her depressed subordinate, Sanada, after repeated work mistakes, she decides to host a home party. The three of them let loose and drink heavily, eventually leading to Sanada spending the night. The next morning, while Haruka is enjoying her usual anal sunbathing, she is unexpectedly discovered by Sanada, who has just woken up.