Okay so I'm back. Ngl I feel like I've read this cuz it's a VERY COMMON NOVEL TROPE. But as for manhwas.... Uhh lots of rape. ML is as much of a byatch to MC as he is to everyone else in manhwas. Anyways here are some novels with this trope:
https://www.novelupdates.com/series/little-mushroom/ - absolutely fantastic series. 100% read. ML just treats MC a bit special because he doesn't understand why he feels like MC doesn't feel human (MC is not human he's a mushroom. He is not transmigrated. He is not reborn. He's just legit a mushroom that gained sentience and wants to find his spore). Super cute, well translated, it's got an official book and translation too if you're interested.
https://www.novelupdates.com/series/mistakenly-saving-the-villain/ - also absolutely fantastic series. MC was a sickly doctor who transmigrated into a BL novel, but MC was a genius, he read textbooks, not bl novels, and he's missing info.... So he accidentally saved the villain and not the protagonist, but the villain is very thankful :)
https://www.novelupdates.com/series/marry-my-iron-buddy/ - just two dudes who fully trust each other and are a power couple. But also ML only cares for MC, because MC was there in his darkest moment <3
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Then there are the series where MC essentially raises ML or helps him a ton when he was a kid:
https://www.novelupdates.com/series/the-reader-and-protagonist-definitely-have-to-be-in-true-love/ -the best one. Western fantasy. Very good, very possessive. Very in line with the plot you want
https://www.novelupdates.com/series/every-day-the-protagonist-wants-to-capture-me/
https://www.novelupdates.com/series/transmigrating-into-a-mob-character-to-rehabilitate-the-villain-plan/
https://www.novelupdates.com/series/the-scum-villains-self-saving-system/ - these 3 are the same. MC is transmigrated into the master of ML and raises him nicely. So ML gets possessive :)
This trope is also way more common in straight series manhwas because of the transmigration aspect. MC saves the villains life when they were only a kid still so the villain then becomes obsessed with MC, and is only nice to them.
Y’all gimme some recs where the ml is like this — is the one pinning for the mc, is more into mc, fluffy to mc but asshole to others by default