Reborn with an Old Enemy on the Day of our Marriage - Chapter 39 - Weighing a Bet

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.

Song Yan, a senior high school student, lost his parents when he was a child. Before obtaining a mysterious and amazing ring, he has been often plunged into a vulnerable position and easily marginalized. However, his life is changed because of the cryptic ring.

- Description from Novelupdates

I am a girl.But no one can know that.In Silvermoor, only men fight in the war, but House Ironfang has no more males to give.To prevent my father from sure death in the war, I wore his clothes and disguised myself as a man to take his place in the army.We won, but the enemy has taken me captive. The Demonic Alpha King who marked me as his without knowing what I truly am to punish me for losing him a war.But now, it is more than a punishment as he is now obsessed and hell-bent on seducing me. He tells me it doesn't matter what skin I wear, man or woman, he'll always want me.I hope to the Moon Goddess that it isn't true.Because I will never submit to him.

Step 1: Inherit a creepy old mansion.Step 2: Unlock a cursed system that makes girls fall dangerously in love with you… just by saying “hi.”Step 3: Learn that if you don’t reject them within 10 texts, something terrible happens.My name’s Ren.And apparently, I’m the “Catalyst for Affection-Based Catastrophes.”(Yeah. That’s literally what it said.)My peaceful new life? Over.Now I’m stuck in a house full of magically unstable girls:A sword-swinging elf.A fire mage with zero personal boundaries.A strict class rep who faints if I so much as look at her.And a witch who cursed the bathroom mirror to spy on me.They’re beautiful.They’re powerful.They’re dangerously obsessed.And if I mess this up, someone’s going to get hurt—maybe me.Reject them too late? Game over.Fall for one of them? Even worse.This isn’t a dating sim.It’s survival of the cutest.Welcome to my life. It's not just a harem. It's a hostage situation.