You've Got Mail: A Cautionary Tale - Chapter 14 - Let Mr D In, Here’s a Good Boy (NSFW)

A mecha otaku is reincarnated into another world as Ernesti Echevalier (Eru). In this world there exist huge humanoid weapons known as Silhouette Knight. Dreaming of piloting those robots, Eru, with childhood friends, Archid Walter and Adeltrud Walter: together they will aim to become a Knight Runner, pilot of Silhoutte Knight.

Several hundred thousand players are trapped in a gritty zombie apocalypse survival game just after game launch. There are hints that deaths in the game might be serving some other terrible purpose in the background of reality…

The main character, Liu Gan, is a quadruple amputee in real life. A quirk in the server code recognized his prosthetic limbs as ‘real limbs’ in game, giving him ‘normal’ arms and legs that nonetheless have the strength and power of steel limbs, and thus far more power than a normal player. With this minor cheat helping him survive the early stages of the game, Liu Gan sets out to find out what exactly is going on, and to endure as long as he can.

- Description from Novelupdates

An ordinary student, a wretched peeper, a cowardly teenager with a kind heart. In a terrorist attack, he inherited the knowledge of countless elites, embarked on a path of God Jagged Tu…

He is an artist!

He is a mathematician!

He is a psychology Doctor!

He is a master of fighting!

In fact, he is a man

Taken off raw site:

A wretched, dirty young man is working during the summer when he was caught up in a mysterious explosion. After that explosion, the young man is then left with the memories and knowledge of dozens of the world’s experts.

He has changed, his heart has become cold, iron-blooded. He became a killing machine, his mind turned mechanical, calculative. Everything goes according to his plans and calculations!

In this magical, slaughterous world, a door is opened for him…

- Description from Novelupdates

“You are mine, and I am yours…”

The world cannot be saved by the victory of a single man. This book begins at the point where the climax should occur; the battle between a Demon Queen who is a little strange and a Hero who is a little curious.

However, not only do these two give up the battle, instead, they join hands to directly challenge the complicated social structure which dictates that humans and demons must forever be in conflict.

This is too reckless right? How can this be done? Undoubtedly, you are thinking that.

Come, please turn the page. You are about to read a story that has never been told before; the story of the Hero… and the Demon Queen.