Mahoutsukai Mana to H no Tobira

In the deepest level of the dungeon.
We found the final "treasure" —

It was the "Daring Swimsuit"

The adventuring party returned to town and went their separate ways. Mana the wizard was changing out of her clothes when she saw the Daring Swimsuit.

"What would happen if I put it on?"

It is a forbidden door that will open to a world of sensual pleasure. Would you like to open it?

(Source: ComicWalker, translated)