Shadow Leveling (Arifureta X OC/Male Reader)

Shun Mizushino was always getting bullied and was suffering by the pain of weakness. However, when he was summoned into a fantasy world, he was betrayed by one of his classmates and was left in a dungeon to rot. But after narrowly surviving, a mysterious program called the System chooses him as its sole player and in turn, gives him the extremely rare ability to level up in strength, possibly beyond any known limits. Shun then sets out on a journey as he fights against all kinds of enemies, both man, monster, and god to discover the secrets of the world and the true source of his powers and way back home to his sister, as he swore that he won't let anything stands his path.