汚れた白さを何と呼ぶ？

It's been three months since the protagonist Tachibana and his junior volleyball club member Kanon Fujisaki started dating. Due to Tachibana's shy personality, the summer vacation is about to pass without any progress. One day after club activities, Kanon was secretly masturbating in the old gym storeroom when Nishijima, the volleyball club's temporary coach, recorded her. Kanon knew that if Tachibana found out, he would definitely dislike her, so she accepted Nishijima's suggestion... (Source: Fanza, translated) Note: Released at Comiket 103.