Sword Of Ryonasis ~Kirsch In Lewd Labyrinth~ by Ankoku Marimokan

Preview

A whole knight legion was literally swallowed by a shady dungeon,
often regarded as the residence of the Evil God. A rookie knightess
Kirsch, left alone by the other knights, gets into the dungeon but
she is cast "magic spell of lewd emblem" there.

Barely given escape by the Holy Sword, she restarts moving forward.