Bokutachi wa Benkyou ga Dekinai: Nagisa ni Usemono Arite Senjin wa Enzen to [X] Suru

ぼくたちは勉強ができない「渚に失せものありて先人は艶然と[X]する」

Bundled with the limited edition volume 14. The episode adapts chapters 48 and 49, which follow Yuiga and Asami going on a fake date, and Yuiga encountering his teacher Mafuyu Kirisu after she accidentally loses her swimsuit top. (Source: MAL News