Some iffier titles that occurred to me.
You must be registered to see the links
(Circle Poison) - It's not called out as a energy drain work, yet it's practically central to the entire premise. Your MC, Batz, successfully bullies an unlucky valkyrie, Lucida, into having sex with him, and unknowingly steals all of her levels in the process (she had meant to gift them to the Hero). At that point Lucida, to get Batz to carry out her mission, agrees to become his slave for as long as he's stronger than her. From that point on, every time Batz sticks his dick in Lucida, she actually claws a level back from him. So progression revolves around returning enough levels to Lucida that you can clear the current content you're doing, but if she ever gets back above Batz she'll fucking kill him. (Unless you can clear the not-so-hidden objective of breaking her spirit, at which point she's actually loyal.)
You must be registered to see the links
(Potato Life) - minor element; only happens in a scene or two. If your MC, Saya, is defeated by mob enemies she'll be taken back to a monster lair to be raped. In the second dungeon there are starfish-looking enemies that not only rape her, but convert her mana into breast milk and drink her. Normally you start monster lair escapes at 1 HP but with your remaining MP, but a starfish lair escape starts at 1 HP and 0 MP. So better have some consumables or you might be stuck there for a while. There's also a troll enemy that might drink her mana but I'd have to check. Aside: There's also a very optional side quest (and by optional, I mean you get red text asking if you're sure) where Saya gets captured by a monster collector and has her powers suppressed until she can escape his mansion. (I also suspect that there was a similar intended plot thread with the corrupt priest, but he got dropped as a possible bad end.)
You must be registered to see the links
(Milk Factory/Frontwing) - strictly a visual novel; there's no fail state and only one choice - picking which of three endings you want - matters at all. But it revolves around energy drain, so fuck it. Heh. Like Miel, Milk Factory basically makes the same visual novel over and over again and are carried by their excellent art. The common theme is you are some lucky jackass who gets into an all-girls elite school and through some sort of authority proceed to turn your classmates, their hot mothers, and the all-female faculty into your harem. In Oppai Academy, you are that world's Haruhi, and the magic school headmaster wants you to speedrun learning magic by having you take it from your classmates. Most of your classmates reject your divinity and object to being your mana batteries, and have to be corrected. This is another setting where magic power can be converted into breast milk. So once you've successfully tamed your target she'll prove her submission by spontaneously lactating, and you'll drink her to take her power. Which you can then leverage to conquer her mother and a related faculty member. I could see this being done as a proper CYOA where you have to trail-and-error through figuring out working target orders, but that's not what they did. You're just actually God and your victims don't stand a chance, though by your decree they'll enjoy it. (Milk Factory stuff is amusing, because the tone is always super-chipper, but what's going on is actually really fucked up when you step back and look at it.)
You must be registered to see the links
(Softhouse-seal/Devil-seal) - another visual novel (and a really short one at that), but it's Devil Seal, so it's nothing
but fail states. The Demon King's conquest of Earth is about 99% complete, but the magical girls (who all became kemomomimi girls after gaining their powers) that appeared as the direct result of his invasion are putting up a last desperate resistance. One trio in particular - a wolfgirl, foxgirl, and catgirl who alternate as your PoV characters - has proved exceptionally annoying, and so the Demon King personally curses them so that they start going into heat, losing access to their powers while in heat, and being further weakened each time they get satisfaction and release from their estrus. Resulting in the girls now being savagely hunted by the small fry monsters they used to crush, while they make a desperate bid to reach and defeat the demon king with whatever power they have left. There's no set of choices where they can win; your choices only determine how they'll lose.
You must be registered to see the links
(Circle Poison) - in combat normally monsters will constantly sexually harass Koyori, and it'll be called out as energy drain, even if it's just unblockable HP loss. Bosses don't do this at all. Also, if you elect to have a defeat to normal monsters end in a game over then after the extended defeat rape scene then you'll usually get some text on a black screen advising Koyori was drained of all of her energy and never seen again.
Edit 3/7/26: Added another title.