This is a tough thing to tackle, more tough than I think people realize. I definitely agree that some more enemy variety would be nice, and there will a few more in the next chapter. That said, there's a kind of tug-of-war between number of enemies and the depth of the art assets involved, since time is limited. A traditional small RPGMaker project might have a bunch of enemies, but all that's required for them is one static sprite. They also often lean heavily on pre-made stuff. I can't do that: everything has to be made fresh. Which means every enemy needs:
-A battle sprite
-A walking sprite
-Face cut-ins
-Battle sex sprites specific to them
A lot of sex rpgs handle this by either having only one sex sprite per enemy type or by having every sex sprite be generic, and thus usable by any enemy. I can't do the first, since my theming tends to a small handful of new enemies per chapter. I could do the second, but there would end up being a lot of repeated and samey battle sex. This would also mean that doing slightly different control mechanics for each chapter would have to be thrown out.
Ultimately, I can have a lot of enemies with fairly similar sex moves and mechanics across all the chapters, or I can have just a couple in each, but with some depth and variety to their sex and hypno mechanics. Considering the kind of game this is, I've opted for the second so far. All that said, I do aim to have two different enemy types (actual, not just palate swaps) on launch with the next chapter, and potentially a third eventually.