I find it peculiar how the game has stuff like hallucinatory parasites, but does not have more traditional equivalents of them like vibrators or shibari. The mechanic for them is at least partly in place due to said parasites
However I'm sure I'm not first one to mention them, so I'd rather expand the topic somewhat
Unlike parasites they could be put on and off in private times and perhaps outside of those as well, with risk of someone seeing the act. Which brings to another point - unlike parasites they could be seen and thus make the NPCs react upon noticing. Also them and some other optional toys could increase the sexual skills while worn. There are some more creative means such stuff could be done in such as in the picture here
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That aside, playing playing with oneself could be expanded in general for some methods of safely or not so safely rising sexual skills based on location, time etc., without involvement of third party (or without them knowing). Unless they find out or are perhaps called to