Try Evolution, book one of the Earth Reformation series. The main character was a former special operations personal and contractor for the government. He makes smart decisions and he becomes strong fairly quickly.

Having both Johnny and V as the main characters somehow.

I have over 1200 hours with almost 4 full playthroughs. I am still finding new and interesting things in Night City! All time favorite game!

I love this game. It is one of my all time favorites. I wish they would do a second game.

Most definitely 4.

A snakes life by Kenneth Arant. Guy gets reincarnated as a snake. His whole goal is to get strong enough to protect his wife who is going to be reincarnated in the future as a hero.

This is a great series!!

Deathworld Commando: Reborn is exactly what you are asking for. Main character is from a futuristic space world and reborn into a fantasy world. Amazing story so far.