Inka: Nikuyoku ni Aragaenai Karada

Despite being married to a young and handsome king, the dark elf queen is left unsatisfied with her husband's performance in bed. Captured human mercenaries, aware of this fact and unable to tear their eyes off the queen's irresistible body, use the knowledge to their advantage when the king leaves the castle. Resistant to the mercenaries' advances at first, the queen quickly gives in, drowning herself in carnal pleasure.

(Source: MAL Rewrite)