Henkyou no Ofuroya-san, Harem ni Naru ~Yamaoku ni Aru Sabireta Onsen no Kounou ga Cheat Sugite Onna Boukensha ni Daininki na Ken~

Deep in the mountains, a young man named Rio manages an old, run-down hot spring. Using his mysterious skill, he adjusts the properties of the waters only to discover that what he thought was ordinary is actually cheat-level powerful! News spreads fast, and soon female adventurers of all kinds flock to the spring. But there's a catch... the waters don't just heal; they also awaken certain desires...