18+ Tower of Etruria

A brave knight named Albion has been sent to recover a princess named Cecelia from a monster-infested tower held by the witch Etruria. Winning her safety (and her company in bed) from a nefarious (but inexperienced) beholder, they must learn to cooperate to face other threats, such as the ninja spy Palmyra and the seductive and deadly Sirena.

(Source: THEM Anime Reviews)