On the first day of middle school, Nayu Hayama accidentally shows her black lace panties during the opening ceremony. Yako Jingūji and Haruka Shiraishi hear rumors of her doing "enjo-kosai" or prostitution, and spot her talking on the phone about uncomfortable underwear to a man who arrives to deliver her some underwear. Curious, the two follow Nayu to the underwear department, but run off when they are spotted...