Multiverse of Marvel - Chapter 720: Beyonders

A man who was once called the world’s strongest agent ended up becoming a teacher after his retirement, to train a new generation of agents. After many years of training his disciples, he was killed at the age of 60 by a secret organization’s ruse and was reincarnated in another world with his memories intact. Though he was surprised by the existence of magic and the strange species in that world, he quickly adapted to his condition as a newborn and took advantage of it. He acquired special magic and gained a massive amount of strength thanks to his rigorous discipline, in order to reach his goal: Resume his career as a teacher which he left halfway through in his previous life. This is the story of a man, who, based on the memories and the experiences of his previous life, became a teacher who travels through the world with his students.

Cut through the road of life and death with one knife, and Hanren slaughtered all those who had hearts!

…

I don’t want to be a knife, I want to be a knife bearer.

I don’t want to be a pawn, I want to be a chess player.

an ordinary person.

But he wants to live out himself in this world.

The unknown road ahead is slim, and the future is unknown; just walking step by step, before you know it, it is already a journey, and there is no world.

The thorny road, the red dust is far away; the clever move, the step is high;

Flatten the sea, turn over the rivers and lakes; clear the blue sky, hold the sword of heaven.

- Description from novelbuddy

Another entry in what you can call the Proto Harem Series: the books written before the Harem Series that take place in the same world.

It’s about a swordswoman whose student is captured, so she goes to rescue her.

WARNING: DARK AND MATURE CONTENT. Readers discretion advised.Serena Alaric wanted nothing more than a quiet life, far from the shadows of her family’s dark past. But when masked enforcers storm her home and drag her into the clutches of the Council of Vitae, she learns her blood is the key to a deadly legacy she never asked for.Lucian Draven is the cold and ruthless leader of a powerful mafia syndicate, cursed to endure unimaginable pain. The Council claims Serena is his only salvation. Yet beneath the Council’s polished facade lies a web of lies, experiments, and betrayal that runs far deeper than either of them imagined.Forced into an uneasy alliance and given a time limit to produce an heir, Serena and Lucian must navigate a treacherous world of power and manipulation, where trust is a rare commodity. As they uncover the truth about the Council’s sinister plans, their hatred begins to give way to something unexpected—a bond forged in fire and blood.But with enemies closing in from all sides and time running out, Serena and Lucian must decide: will they fight their fates, or embrace the dangerous connection that could either save them, or destroy them both?