I'm not sure that these exactly fit your goal, but might as well mention them.
Valkyrie Destruction by Poison. Only exists in Japanese unfortunately, but not hard to MTL.
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You play as a thoroughly evil bandit that is accompanied by a valkyrie who he has stolen 60 levels from, making her only level 1. Every time he has sex with her, she manages to steal back 1 or 2 levels, which can be nice so she'll be a better helper in battle. But if she gets more levels than the MC, and manages to break his control, you get a bad end.
Curse of Kubel, translated by Kagura Games on Steam, originally by Yasagure Kitsuenjyo
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It's Netorare. You play as a female mage who has a boyfriend, but an evil jerk has cast a spell on her so she can't use her magic unless she has sex with him, and only can use a little even if she does. She has to fight her way to a forbidden underground library to seal it like 4 times. Each time, if she runs out of magic before she can get there, she has to go back and get raped by the evil guy. Then start over. Different endings depending on how far it goes.
It has great artwork, but there is only one person she has any scenes with.