Jack Lincher, a war orphan who scrapes by scavenging corpses on old battlefields, uncovers a scorched grimoire that awakens his memories of a past life as a modern-day Japanese man. He realizes this world is the setting of a game he once played. With only a few years until the game’s main story begins—a full-scale war involving seven nations—Jack resolves to climb out of his desperate life, even if it means using the very war that took his family. He is determined to avoid the near-inevitable doom that awaits this world. Yet, after long and painstaking effort, all he manages to master is the lowest tier of combat magic—barely strong enough to take down a single person—along with a highly situational “self-customized magic.” Unyielding, Jack leverages his modern knowledge to refine these “worthless” low-tier spells, elevating them to what could be called **Calamity-class**. In time, his name begins to spread across the battlefield. …Little did he expect that along the way, he’d catch the attention of some seriously dangerous people.