The Ruler Of Darkness - Chapter 7Book 5:

A high-schooler who loves playing FPS games were reincarnated in the fantasy world. And usually, those who were isekaid were blessed with overpowered magic and a legendary beast. However, our main character is different.Instead of those things, he awakened a shop system where he could purchase American freedom! And since modern guns is as good as magic, he decided to make full use of this ability and make a name for himself in this new world.Fireball? Cute. My M203 grenade launcher makes a bigger boom.Summoned beast? That’s nice, I’ve got a UAV with thermal optics.You can split oceans with magic? Cool. I can erase cities with a nuke.Whatever overpowered spell you’ve got, I’ve got something better.

On the surface, he is the aloof and standoffish patriot whose sole purpose is to serve the nation. On the darker side, he is an invincible, powerful and mysterious man.

A seafood chef inexplicably transmigrated into ancient times. Even though he landed in a family with a nobility rank, and theoretically was supposed to be rich, the most valuable thing in the house is a grey donkey…
Su Yu stared at the sky helplessly; in order to support the family, he could only take up his old profession and go out to sell fish.
Unfortunately, the royal family selected concubines from both genders. Even as a poor noble, he had no choice but to attend…
DISCUSSION TOPIC: Will I be selected if I display my fish-slaughtering skills?
“Meow!” His Imperial Majesty shook his tail.

- Description from Novelupdates

In the post-apocalyptic age, men were damned.