I can't say I blame the creator here... It's a case of too much ambition, and simply putting way too much H-content for each monster in a decent platformer.
In a regular platformer, making a new simple enemy requires an attack animation, a moving animation, a "being hit animation" and a standing animation. Depending on the enemy and game type, you can sometime get by with even less than that.
In this game, every monster has (I think) 6 "aggress" animations. That's more than double the animations you need to make a functional monster gameplay-wise! Not only that, all those animations requires also animating the main character and have them interact properly, which makes every single of those animation far more work. Wasn't there some "struggle" animations on top of that too?
So to add a new monster type in Mitsuko X, I'll assume that the time-spent ratio was roughly 10% make function and 90% h-content... With a ratio like that, it's pretty much impossible to build a good, long platformer with a decent enemy variety. It was a good concept (and the implementation was actually quite good, impressive for one person on his spare time), but it's pretty much impossible to pull off long term without having an extremely dedicated team with a ton of time to spend on the project.
