Mahou ga Tsukaienai Mob Chara ni Tensei shita kedo, Ore dake Tsukaeru "Saikyou Kengi" de Nariagaru: Oshi no Akuyaku Reijou no Ani to Natta Otoko wa Hametsu Flag wo Tatakiri, Game Sekai de Musou suru

Story

Soldo, a young boy, is reincarnated as a countryside noble in the world of a magic game. He is excited about the adventures he will be having in the game world he has played countless times in his previous life, but he is confronted with the shocking truth that he has no talent for magic...! Unable to use magic, Soldo is destined to live as a worthless mob character with no impact on the story, but one day he discovers a book about "secret swordsmanship" hidden within the game!

Synopsis via AniList (English).