Manga Kyou Senshina Mob Mujikaku Ni Honpen Wo Hakai — Suru Manga Best

The manga (translated as The Mad Mob Characters Unknowingly Destroys the Main Story ) is a refreshing take on the "mob character" reincarnation trope. While many isekai stories focus on a protagonist trying to follow a game's script to survive, this series centers on a "mad warrior" who completely derails the plot through sheer oblivious chaos. Plot Overview

I’ll assume you want a about the "genre / trope" where an overpowered side character (who thinks they're just a mob) unintentionally derails the main plot. The manga (translated as The Mad Mob Characters