Katoptron is just the Greek word for a mirror. Given that in the Japanese version it is already called such, and they probably have even less chance of knowing that word than speakers of European languages, then I see no reason to overcorrect it in translation. You wouldn't change necromancy to undeadmancy.
guitarhero47 To share some maybe helpful recommendations of my own. If you are able to really get into the feel of power deterioration and eventual helplessness, while not getting immensely triggered by going against basic gamer sense - you can totally go wild on the aforementioned Quartz Amethyst & Quartz Emerald. They are a great experience in that regard, but their actual battle gameplay is a bit lacklustre.
Meanwhile, if looking for more gameplay-oriented erotic battle games, I would say for top picks:
- Maken-shi Sara (or Magic Fist Sara) - A really solid and fun game with nice style. Perhaps the closest to Luna in terms of aesthetics, although very different approach to mechanics.
- THE TALE OF UNDERCRUST ~The Last 7 Days of Hasumi~ - Incredible game in many ways. And if liked Luna having tons of flavor texts for random objects and the whole collection tab for anything and everything. Hasumi is a game where you enter for lewds, then stay for geology trivia.
- Taima Miko Yuugi (or Shrine Maiden Exorcist?) - Don't get discouraged by the unusual artstyle, this game has possibly one of the best battle systems in an erotic battle game. And good comedy to boot.
- Jumble Strikers - I wouldn't put it as high as the other three or Luna, but it is still a neat, good looking, game that is worth distinguishing from the crowd.
As a side note, you may see a lot of people mention Celesphonia here and there and it may look as if it was an erotic battle game - but it just isn't. It totally looks like it should have been, but that is not the case.