Isekai Maou to Shoukan Shoujo no Dorei Majutsu - Volume 8 interlude 1

Also known as Venerated Venomous Consort. In a modern world, a professional assassin was murdered by her beloved and found herself revived in an ancient world as a general’s daughter with a weak physique. She was engaged to a prince, but because she did not have a nice appearance, her fiancé and sister attempted to kill her. Although she had to struggle to survive, there were also those who unconditionally loves her that supported her in her time of need.

How does she intend to adapt and survive in such a foreign and hostile world? Follow Gu Xijiu on her journey to discover her one true love!

- Description from Novelupdates

What happens when a scientist from a futuristic world reincarnates in a World of Magic and Knights? An awesome MC is what happens! A scientist’s goal is to explore the secrets of the universe, and this is exactly what Leylin sets out to do when he is reincarnated. Dark, cold and calculating, he makes use of all his resources as he sets off on his adventures to meet his goal. Face? Who needs that… Hmmm… that guy seems too powerful for me to take on now… I better keep a low profile for now. You want me to help you? Sure… but what benefit can I get out of it? Nothing? Bye. Hmmm… that guy looks like he might cause me problems in the future. Should I let him off for now and let him grow into someone that can threaten me….. Nahhh. *kill*-

Alternative: Leylin is transported from an advanced technological era into a medieval world— except there’s magic. Equipped with “only” his quick wits and an A.I. chip fused to his soul, he sets out to become the most powerful magus the world has ever known. In a land divided into the Light and Dark Magi, the weak can either be cattle or disposable slaves. Only the strong can determine their lives, and only they have the luxury for virtue. Yet strength is only a tool for Leylin, like any other. His goal, in the end, is his own.

Jacob Steve, an Old Man, died at 116 after living a whole life.

But Jacob always had a dark side, which he always suppressed and hid from others.
However, in the later years of his life, when death was inevitable, he understood there wasn't any point in having wealth, knowledge, or desires if you couldn't have a life to enjoy them.

He became obsessed with fabled immortality and devoted his reaming life to extending his fleeting lifespan, but just like any other failed.

However, he mysteriously got another chance at life and found a way that led to fabled immortality.
But he was also forewarned that the way led to it was filled with blood and darkness!

In the end, Jacob chose it anyway with no way of going back, and it was also the start of his suffering and his icky, brutal journey toward the 'Immortality' he wanted so badly!

Alex was an ordinary person with the dream of one day being transmigrated to a magical world.

But what he didn't expect is that he would be transmigrated to a world much more than that, a world he knew very well, but instead of being given a system that would empower him, he was given a system that allowed him to make games, and the more people played, the more powers he would get.

Tony Stark: I hate this! I can do in real life everything this Watch Dogs guy does, but why can't I stop playing?

Hulk: HULK HATES DARK SOULS!!! HULK SMASH DARK SOUS ARRRHHHHGGG!!!

Nick Fury: If any agent can't complete the Hitman game by next week, that agent will be fired from the Shield!

A world of superheroes, but who controls everything is "only" a game developer.