One Piece: Unreal Adventure - Chapter 15: Out cold

In the early world of immortal cultivation, there was no physical cultivation among immortal cultivators. And a top bodybuilder who came from the earth has opened up a new path here and became the ancestor of physical training.

- Description from novelbuddy

She was originally a puppet of her family. Pursued by the police for being a business spy and hitman, she was betrayed and fell into the sea.

When she opened her eyes again, she had turned into an ordinary high school student. Because of a disgraceful birth, she had been crowded out by her relatives. Because of inferiority complex and antisocial behavior, she was bullied by her classmates.

But now she is no longer someone who acts timid. Cheat her, and she will break your bones.

She possesses formidable Jade pupils capable of seeing through walls. Other people have difficulty breaking through jade, their sight for antiques is based on gambles, but she only needs a look.

An undertaking begins as she creates legends in the world of business.

Once upon a time, they laughed at her poor and destitute state. Now looking at her net worth of 10 billion, it can’t be explained.

To the relatives that come to hug her thighs, she must apologize: “We broke off relations long ago, so get lost!”

- 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 ͡°)

“I hope you don’t fall in love with me, because I won’t be taking responsibility,” warned the young man. “Don’t worry, I won’t fall in love with a body double,” the employer dully replied. Yet, both of them forgot what they had said.