Toaru Majutsu no Index: New Testament - Volume 17, Chapter 1: Or Cutting Off Leads to Diffusion - Gray_City.

Two years ago, Nina married a man she had never met. She didn’t know his name or his age; she knew nothing about this person she was married to. Their marriage was nothing more than a contract with conditions, and one of the clauses was that she should not sleep with another man.

Yet, Nina lost her virginity to a stranger when she knocked at the wrong door one night.

With the compensation she had to pay weighing her down, she decided to draw up a divorce agreement on her own.

When she finally met her husband to hand over the papers, she was shocked to find that her husband was none other than the man she had “cheated” on him with!

At the age of 15, He Jin found himself a “husband” in an online game, their love was filled with loving affection and sweetness. However, because his study was being interfered with, his parent cut off the internet, he didn’t even have a chance to say goodbye and had to disappear from the game.

8 years later, the online game in the past was about to come out with a revised edition and turned into a virtual reality game. He Jin decided to login again and unexpectedly discovered that his “husband” had become a powerful player and ranked number one in the whole server, moreover, he had not divorced him!

However, the husband that was abandoned by He Jin for eight years, his initial impression of him was that of a pure boy, but now he seemed to somehow have become…….a little evil?

- Description from Novelupdates

Dual cultivation isn't a choice; it's a necessity.

After being struck by a truck like most lucky protagonists (or unlucky ones), Vaan found himself transmigrated into the body of an orphan in the world of witches and demons.

However, they didn't always exist.

Demons terrorized the world ever since the Gehenna Realm descended over 300 years ago. but along with them, came mana, giving birth to witches to combat these demons.

Since then, the world of men was dominated by witches, establishing the seven witch kingdoms, which safeguards at the forefront of the demon invasion.

In order to survive in the matriarchal society of the witch kingdoms, Vaan, like all other men who cannot use magic, had to learn how to service the witches to survive.

Nevertheless, it did not come without its own benefits.

Years of research have led the world to the discovery of intimacy between men and women could increase the witches' mana absorption.

But at the same time, men could absorb some of this mana to improve their physique and lifespan.

Thus, since then, an intricate relationship was formed between men and witches in the red-light districts. Love became casual, and dual cultivation is common.

As a prodigy in the art of pleasing women, Vaan lived a smooth two years since his transmigration as an orphan.

However, everything came crashing down in a heartbeat one day when his life was nearly taken, and Lady Eniwse whom he served went berserk.

Even so, that was not the end.

With the awakening of the Witch Hunter System, watch how Vaan takes on the world and becomes the lord of witches.

=====
Note: Contains lemons.
Hunting witches does not necessarily imply killing witches if you know what I mean ( ͡° ͜ʖ ͡°)

Su Wan is a Realm Destroyer. She shuttles to different time-spaces using the identity of the “Cannon Fodder Ex-Girlfriend”, dedicated to plotting how to happily tear apart the male protagonist and the female protagonist. –There’s no such thing as protagonists who can’t be torn apart, only Ex-Girlfriends who don’t work hard enough~