Magika no Kenshi to Shoukan Maou - 5.2.1 — Discarded Fox Diary

There is a very strange restaurant in the City of Sin.

“There are no heroes. In life, the monsters win.”

...

In 2106, [Mayhem Online], a fully immersive VRMMO game, was released. Soon, it dominated the world's economy when people could exchange the in-game currency with real-life currency and vice versa.

In the year 2107, Flynn Grey, a 22-year-old college dropout with an ambiguous history, joined in the fray of billions of people that had already started playing [Mayhem]. Hoping to uncover the game's secret and earn a fortune, he spent months on adventures without fruitful results.

For better or worse, Shura, Flynn's in-game character, ends up in a great Wyvern's den, acquiring a hidden class and a monstrous race. Join him as he defeats his past and paves his way into becoming a true legend in both worlds.

This novel is also known as Long Live the Mad Wife!

Daughter of the Feng Family, born a waste. Forced to marry a fool in an attempt to expel evil influences. When the first killer from the 21st century possessed this body, the sky and the earth surged. She was indifferent and cold-hearted but she let her guard down around him alone. She thought he was a pleasant sheep but didn’t expect him to be a gray wolf in disguise!

- Description from Novelupdates

A fighting genius.