BL Isekai

Otaku shut-in MC wakes up in another world where the Demon King claims he'll become his maiden and bear their children.

Sales assistant MC is "Truck-kun'd" into the world of a novel he worked on selling as a minor character that dies in the plot after committing a crime. Does his best in the new world to avoid getting arrested or causing trouble.

MC is reborn as a crown prince in a game and knows the events of the game about to take place. Attempts to help the hero level up before the game begins.

MC gets "Truck-kun'd" into another world, and spends the story trying to find his way back home.

Man is reincarnated as a god in an alternate world with a magical system that acts like a game system and meets a demon king.

Disclaimer: It's really bad. Very rushed and gives you whiplash with how fast it is. Also trash characters. Read at your own peril.

Not exactly isekai, but couple rebirths into multiple lives forgetting each other until they see a certain trigger, and then they remember everything. This is one of the cycles, where they're idol and manager.