Ossan Boukensha no Okureta Eiyuu-tan: Kansha no Suburi wo 1-nichi 1-man Kaishite itara, Kensei ga Deshi-iri Shigan ni Yatte Kita

Born as an illegitimate child, Guy Gullveig endured years of torment at the hands of his half-brother before finding refuge with his grandfather, a retired adventurer living in seclusion deep within the mountains. To mend the boy's battered body and spirit, the old man prescribed a simple regimen: daily sword swings. Even after his grandfather passed away, Guy never abandoned the routine, faithfully executing ten thousand practice strikes every single day until he reached middle age. Guided by his late grandfather's final advice, he eventually leaves the mountains to pursue a new life as an adventurer in the city. What Guy fails to realize is that decades of relentless repetition have forged him into the most powerful swordsman alive. As he travels and selflessly lends his aid to others—from Sword Saint Altina and guild receptionist Lilina to the noble Lady Celis—those around him gradually awaken to the staggering reality of his strength. This fantasy epic follows a kind-hearted, older adventurer who unknowingly perfected his blade through sheer dedication, allowing him to effortlessly cut down the world's mightiest foes without ever recognizing his own unrivaled power.