there's such a thing ? can you recommend some of these bls ?
There's plenty, try these, they're my favorites:
Every day the Protagonist Wants to Capture Me (MC wakes up as the villain character and ends up with the protagonist)
Scum Vilain Self-Saving system (Completed: I'd suggest reading the reviews/spoilers. the beginning of the story is nice, but there's a part in the middle that ruined the story for me, Villain character MC.)
In these, the transmigrator doesn't end up in the body of the villain, but they're all great:
The Reader and Protagonist Definitely have to be in True Love (completed)
Transmigrating into a Mob Character to Rehabilitate the Villain Plan (AKA Villain Rehab Plan. Completed - MC ends up with the villain)
I’ve Led the Villain Astray, How Do I Fix It? (MC ends up with the villain)
Picked up by the protagonist of a Tormented! MC novel (MC ends with the protagonist)
Never Thought You’d Be This Kind of Hero (slow to update, but hilarious, the MC starts off playing a game, but once he kills the demon king, he's part of the world and can't leave.)
There's more, but these were the best of what I read in Isekai bl. They all have a page on novel updates, links to read the stories are also there.
I think it's funny how I really love transmigration novels when it's bl and the 'villain' ends up with the protagonist, because there's no heroine who has to take the fall and be an antagonist. They're just usually ignored and not part of the plot. I just can't trust the hetero ones.