Slimegirl

The Slimegirl is a non-standard NPC encountered in the waterfall region of the Woods. She is usually harmless, sometimes assisting in your cleaning by licking semen off of you. But, if there was enough semen (or if lactation fetish is enabled, every time), she will decide to join you in your adventure, and try to swim up inside you. A number between 0 and the dexterity of the player must be higher than 7, or she'll get inside. Wearing swimwear makes it much less challenging to escape from her.

Once inside, she increases your belly size and weight by a medium amount, but she immediately consumes any and all semen that enter your asshole, preventing you from ever overfilling. If you don't receive any anal creampies for a long time, she gets hungry, and can start to negatively impact you in an attempt to get you to feed her. Things she can do include temporarily increasing your sex and semen addiction scores, permanently increasing the size of your hips or butt cheeks, making you very aroused, and (when near death) increasing lactation rate, increasing your need to pee, and increasing the size of your breasts. If she dies inside you, you will have your sex and semen addiction each lowered by 2.

If she's friendly (not hungry) and inside you, you can learn a skill from her, if lactation fetish is enabled. You can learn how to drink milk directly from your own breasts.