It's about a demon lord who is interested in someone. He somehow becomes interested in sex between two guys but doesn't know anything about it, so he decides to research about it. One method of how he researches is by calling over two guys and have them perform in front of him.
Transmigrating into a Mob Character to Rehabilitate the Villain Plan ? The scene you’re searching for is either in volume 3 or 4 I just now realized the title lmao sry my bad
khh.. I read a manga similar to that just now!! bl of the space. https://myreadingmanga.info/soutome-emu-bl-of-the-space-eng/ probably not what you're asking for... I think I read that webtoon before too... but I cant remember