During the fourth dungeon the player's penis is transformed into a vagina whenever they are inside of it. It reverts when you exit the dungeon though.
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While it could be done through Beatrice quite easily the issue is that then every sex scene in the game afterwards needs to account for whether you have a penis or a vagina, and I've learned from some other things I had in the game earlier on that writing variations like that for every scene is something I would not enjoy doing at all, so it isn't planned. I intend for it to be an option at the end of the game though.