Well, it's by design. The basic gimmick behind the series is that the main character is a patron of a brothel that takes their payment in actual levels rather than money. They're basically all 'sucubi' with some form of the level-drain technique. (In quotes because most appear human and a few are other monster girl types)
So if you play the game without cheating, you're leveling up constantly and turning those levels back in for scenes. And if you like femdomy stuff in the same flavor as games like monster girl quest, then those sceenes will likely appeal to you. I think a couple of the artists worked on both games, even.
The problem, (in my opinion,) isn't so much that there's grind, it's that in the last couple games the creator didn't bother to do anything special with the gameplay. Most of the good RPG maker games take some steps to customize the formula. New battle mechanics. Special skills, interesting enemies. Anything along those lines.
But this last guy's game was basically stock RPG maker all the way through, with the default database enemies, skills items and such with barely even having tweaked numbers. Makes the combat pretty boring.
