Yui's father died after remarried to Horai. Yui and Horai, who are stepchildren, are close in age and are mother and daughter-in-law, but they got along like friends and lived together. Unable to forget the ecstatic expression of Horai, who had been tied up before, Yui hides her feelings for Horai. One day, the two of them find out that they both feel the same way... and get stuck in the swamp even though they know they shouldn't. Rich lesbian play, hard spanking, hanging bondage, and enema to test and confirm each other's feelings.