I Breathe Euro - Chapter 206: Synthetic Aether.

When an S-class elite assassin-raised captain of a special ops suicide squad comes home from a high-stakes Africa mission, he finds himself offered something that could potentially set him up for life- a curious assignment that he could use to finally exit his days of war and slaughter.

Then placed into a high-school setting, Lin Yi is tasked by the chairman of a top-tier multi-billion company with bodyguard duty for non-other than his own daughter, a certain little Miss of said high-school.

His enemies, once ranging from drug lords, mafia bosses, political figures, and national leaders, are soon replaced with spoiled kids who happen to have rich papas and mamas, and Lin Yi finds his intense expertise and high-threat skillset misused, and very underwhelmed…

But he does get a harem cast as diverse as his old enemies, so Lin Yi decides that, for the sake of messing around with girls as an invincible entity in a down-leveled environment, leaving his bloody and death-filled war days behind is something he’d definitely want to strive for.

- Description from Novelupdates

First World : CampioneCurrent - Second World: High School DxDThird World: ???Reincarnated into the world of Campione! Haru Kasugano, our hero slays gods and ascends as the mightiest Godslayer. He battles powerful God-Kings and Campiones, claiming victory after victory. Whatever it is. [Wealth, Power, Beauty] he has it All. Watch him grow stronger as he travels into new realms like High School DxD and the Fateverse, leaving a trail of defeated gods and captivated hearts in his wake.

Alternate Title: The Snake Goes Ara AraBy cruel trick of the fates, intervention of stupid gods, or just the apathy of an uncaring universe I find myself woken up as Orochimaru just after he had possessed a woman for his new host. Now I need to find a way to turn this hoard of sycophants and psychos into something that will not only keep me from an early grave, but also how to change it to a force of change in this messed up world.

Keith, a regular office worker from Earth, suddenly transmigrates to the world of the novel he had been reading for the past decade. The new world, which was also called Earth, was slightly different. People with various powers existed who were called awakeners, making this world comparatively dangerous and also mysterious. While he was thrown into the novel’s world, he was also given a mystical ability to grant systems to other people. Armed with his special ability, he slowly climbs up the power ladder by taking “taxes” from the people he would give systems to. The only question that remained, was what would a realistic normal man, when faced with a similar minded protagonist, do when their goals opposed each other.