itch.io

Basically, they're little things that can activate in events or with certain actions as far as I can tell. For instance, you can get the cocksleeve one for Pixie if you have sex with her in her smaller form... I didn't even mean to discover that one, honest.

GamingBard is correct - they're called Quirks, and they act as a kind of achievement list as well as gating content in-game. For example, if you like "cocksleeve" content then unlocking it with Pixie tells the game you like it and would like to see more. If you don't unlock it via your choices, then the game assumes you're not into it and won't give options/events for that kind of thing.