Global Reincarnation: Only I Know the Plot - Chapter 42:

After Reincarnating into Naruto World at the Warring State Era as an Uzumaki, Masahiko thought that he got a useless System. He lived for 48 years as a normal, below average Uzumaki Shinobi.

That changed when he finally knew how the system works the day of his 49th Birthday!

- 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.

I had nothing left to live for.No family. No friends. No future.Just a shattered soul wandering through a world that had already taken everything.Then I died.And that’s when everything changed.I woke in a world of light. A void between realms. A place where gods whisper and broken souls wait to be judged. There, I met Ashen Crimson—a man who had once been worshipped, then feared, and finally cursed by the very gods he had defied. A tyrant who had destroyed his own world.But now, he’s offering me something terrifying:His life. His past. His power. His chance to make things right.The catch?The world of Zerawell is fractured.Ashen’s name is soaked in blood.His fate is sealed—exile, ruin, and eternal hatred.And now, it’s my name.Because I’ve been reborn as Ashen Crimson, heir to a house that both reveres and reviles me. A noble with dormant shadow magic, a shattered reputation, and a cursed destiny I never asked for.But I’ve lived a life of pain. I’ve walked alone through hell already.And I won’t follow his footsteps into madness.With a divine system familiar in my soul, a second chance burning in my chest, and the memories of a monster as my burden—I will rewrite this fate.Let them call me villain, disgrace, or traitor.I didn’t choose this story.But I’ll finish it.Even if it kills me.

Almond Crowshade was the last surviving human in a dying world whose people failed to conquer the Grand Abyss Labyrinth’s 30th floor in time. The world was getting destroyed, and Almond was the last one challenging the 30th Floor multiple times despite the imminent destruction of the planet. He ultimately defeated the Floor Boss on his dying breath by achieving a true awakening, acquiring an X-rank Trait that signified limitless potential. Alas, he won but there was no home or future for what he fought. But a mysterious figure arrived there, feeling pity and amusement. “This is too precious and fun of a toy to let it rot here. You shall reincarnate and climb up to make things interesting.” [Transfer to another world commencing…] [Your memories will be sealed, and you will reincarnate in another world that has welcomed Grimworld’s tutorial like this one. Clearing each floor of the Grand Abyss Labyrinth will unlock a portion of your memories, until the 10th Floor upon which you will gain your full memories.] ‘I’m giving you a second chance. This time, you must clear the Grimworld’s tutorial and step onto the big game to make things instresting and entertaining.’ [Good luck.]