BL Isekai

MC Prince is betrayed and killed by his good friend in a final, tense moment, then suddenly wakes up in his bed in the past.

Disclaimer: It isn't strictly isekai, but there's a fantasy setting and reincarnation, so I've added it.

Rebel leader on the run in an enemy nations castle somehow finds himself in a room with a blind-folded omega in heat that seems to be almost expecting him. They have sex, and later find the rebel has gotten the omega, who turns out to be the emperor, pregnant. They make a truce until the baby comes, for the rebel's freedom.

Disclaimer: Omegaverse, but a weird one. The nations are so far apart, even knowledge-wise, that it's basically like the rebel is in another world.

Barkeep MC has special tears that turn into very powerful magical gems when he cries, and this secret is revealed to a knight who blackmails MC into crying around him in order to gain the gems and sell them.

Disclaimer: It isn't an "isekai", but it's another world supernatural adventure in ye olde world, so I'm adding it.

MC gets Isekai'd to another world instead of his sister to be a "maiden" for a mage, which involves having sex to give the mage an unlimited source of magic power.

MC "hero" of the nation, and the Kingdom's best night, meets and begrudingly falls in love with the prince of the demons, his sworn enemy.

Disclaimer: Shounen Ai. Also not technically an isekai, but it's ye olde world "another world" vibes, and the hero and villain both have to "adjust" to each other's worlds, so I'm adding it.

MC gets "Truck-kun'd" into the manga he helps his sister draw as a side character.

Disclaimer: Omegaverse.

Another case of the MC being "Truck-kun'd" into a BL game world. Unfortunately, he's straight, and tries his best to avoid what he thinks is his fate as an Uke-looking character.

Spoilers: MC wakes up 28 days later style in a room alone. Turns out the apocalypse has happened and Zombies roam. Finds a mysterious man who's seemingly calm about the situation, and helps him survive.

Disclaimer: Rebirth. The mysterious man is calm because he's lived it multiple times, which all ultimately end in failure, with the MC waking up in his bed to start the cycle again. Not Isekai, but the rebirth thing is there.

MC and his childhood friend are both "Truck-kun'd" into an otome game for women where the only option to clear the game and escape is to finish a route with one of the love interests.

MC Otaku makes a character on his game, who then emerges from his computer screen and becomes real. It's largely in the real world with a character from a game, but MC does eventually go to the other world as well.