1Rm’S Gigant Rider summary:

Read manhwa 1RM's Gigant Rider / 1RM Reincarnated with memories of the 21st-century Earth, Kang Geohan becomes an unnamed commoner in the continent of magic and steel, Laniacea. In order to escape the life of a virtually enslaved commoner, he must wield the "Stone of Demonhood" to become a Period Rider. "Shoulders back! Squeeze those buttocks! Breathe deeply below the belly!" Using the knowledge from his previous life as a trainer, he accumulates magical power like exercising, climbing the ladder of the strict social hierarchy. Experience the explosive growth akin to a steam locomotive and witness the intense battlefield where steel clashes in the webtoon comeback of "1RM's Period Rider."