BL Isekai

Emperor is assassinated and reborn as a slave with his full memories and skills as emperor. Meets the current emperor who takes an interest in him since he resembles the previous Emperor, not realising it actually is him.

Overworked corporate slave is transported to another world, meets an elf that mistakes the man for his dead lover. There's a magic spirit that does things for the office worker and the office worker calls it Alexa, lol.

Tokyo ganster is killed and reborn in his favourite video game, as the assassin meant to fail an attempt to kill the game's final boss. Instead, the gangster decides to help the final boss.

A corporate slave is transported to another world by mistake whilst trying to save a woman being isekai'd. Instead of enjoying the good life, he demands to work and have a job, and ends up being better than most of the staff there. However, he has poor health and doesn't look after himself to the point of collapsing, attracting the stoic knight-captain's attention.

The traditional tale of story "Journey to the West" but a person is Isekai'd after death into the character of the Monkey King in the story, as "punishment" for his sins during life.

Yankee is transported to another world, where Omegaverse is a thing, and is found to be the King of the country's fated pair.

Disclaimer: Obviously, Omegaverse.

MC literally walks into another world somehow. Nothing much has happened in it yet, other than establishing this world has people with animal ears, and the MC is somehow there. Also, that he is a "sub", and establishing the Subverse universe for people new to it.

Disclaimer: Subverse.

Celebrity MC commits suicide after his lover abandoned him after an acid attack and a fall from fame/public image and scandal. Somehow finds himself back in time, determined to get revenge and survive this time.

Disclaimer: It isn't really isekai, but he knows large amounts of detail that are generally seen in Isekai, so I added it.

MC "con-man" with a silver tongue finds himself in another world, where people mistakenly believe he is a god because their bible, essentially, prophesized that someone with his intricate belly tattoo would walk among them as their god some day. MC plays along, hoping to live a life of luxury as their god, el dorado style.

MC "dies" and becomes a character in his friend's otome video game as the villainess's father. Whilst attempting to ensure his daughter has a good life, through bullshit reasons, he must have sex with people or he'll die. Because isekai.