I agree with this, this has some great implementations of a lot of my fetishes like consensual possession, slime girl bodysuit, etc. but it's missing pregnancy/unbirth as a status effect to make some of them perfect, the rock spitters and slimes should be able to invade Celica's body, the insects should have oviposition, and the jellyfish should be able to cum imo, cause right now it feels like things just have sex with Celica with no purpose other than increasing the lust meter.
Of course there are some people who would not want this, so it should be a voluntary toggle of some kind. Maybe reaching 100 lewdness gives you an item or option setting for it, and you can specify to Nel that you wanna use it when she's taking you for a joyride.