If you are referring to the manga version by Ryuuichi Shidzuki: Volume 10:
" refers to the 10th episode of the adult anime (hentai) series Isekai Harem Monogatari , which was released in late 2021. Series Overview isekai harem monogatari 10 2021
The group discovers the source of "The Severance." It is actually a summoning ritual conducted by the Kingdom's nobility to bring more heroes from Earth to use as soldiers. The "Calamities" were the failed defenses of the planet trying to stop the summonings. Kaito realizes he is part of the problem. If you are referring to the manga version