The Regressor Can Make Them All

Lee Se-Hoon, the blacksmith of humanity's last desperate united force, fought against the demons until the very end. However, the result was mutual destruction, with the world coming to an end. The moment he took his own life over that futile conclusion—
“…What is this?”
He had regressed to his days as a candidate at the hero training institution, Babel Academy. Having obtained a second chance, he swore to use anything as material to gain victory this time. Anything at all!

Original Novel
Official English