Demon Slayer! Returning Forged Blades, Finding Shinobu Kocho from the Start

After transmigrating into the world of Demon Slayer, Lin Moyu only wants to be an unremarkable swordsmith. But the System is always acting up! With the earworm chant of “Big hammer, eighty! Small hammer, forty!” ringing in his ears, he somehow becomes strong enough to shatter mountains. A charcoal seller he meets by chance teaches him a breathing technique for fitness, which turns out to be the legendary Sun Breathing? A wooden puppet he casually makes is so terrifying that a pale, overworked salaryman passing by flees in a panic? It’s only after he takes in a gravely wounded, near-death purple-haired girl named Shinobu Kocho that he realizes his leisurely life at the forge may have already turned the whole world upside down!