Another world reincarnation. It’s also a game world.
Protagonist? Rival? Villain? Important character in an event? Too bad. He’s just a mob. He doesn’t even have a name in the game. He’s not even a villain’s crony or anything. He’s truly just a mob.
And it’s not like he has played this game very much. You might think “Why such a character?”. You might also think “he must have at least some backdoors to cheat through” or something like that.
In such a world, Clueless Berserker Mob even participates in the main game.