Bokutachi wa Benkyou ga Dekinai!: Chapel no Kane wa [X] wo Shukufuku Suru

ぼくたちは勉強ができない！「チャペルの鐘は[X]を祝福する」

Bundled with the limited edition volume 16. The episode features an original premise where Fumino, Mafuyu, Uruka, Rizu, and Asumi are taking part in a wedding ceremony. (Source: MAL News)