The slavery premise isn't window dressing here, it's the entire engine, and the show commits to that friction in a way most ecchi won't. Yuuki's power forces him into a genuinely uncomfortable dynamic that the story actually uses for something other than titillation once it finds its rhythm around episode 5. The action animation is sharp enough to matter, the female cast has actual weight beyond their designs, and by the end you're invested in why these two people need each other despite how it started.

Yuuki Wakura is finishing school and dreading an ordinary future when he is pulled into Mato, a dangerous other dimension overrun by monsters called Shuuki. He is rescued by Kyouka Uzen, chief of the seventh unit of an all-female force whose members draw supernatural powers from Peaches, fruits of Mato that only work for women. Kyouka's own power, Slave, lets her control a living being and draw out its strength, but the monsters she has used it on have always been weak. Surrounded by Shuuki, she tries it on Yuuki, and his slave form turns out far stronger than she expected. To help fight the monsters and save the world, Yuuki must serve as Kyouka's slave, in battle and at home. The series mixes action, fantasy, romance and ecchi.