The "Reaper" of the battlefield returns to his middle school days—Masamune Kurona is a mercenary capable of single-handedly turning the tide of war on the battlefields of East Africa. Faithfully adhering to his father's strict teaching—"Abandon your free will and just follow orders"—he lived his life as the ultimate "tool." That is, until a sudden betrayal during a mission ends his life.However, instead of fading into the afterlife, he opens his eyes to find himself sitting in his middle school classroom from 15 years ago."If I could just do it all over again, I'd do things right..."Carrying the regrets of his dying moments, the ultimate former mercenary decides to finally use his "own free will" to completely crush the evil and bullying lurking within his school. A thrilling school-life revenge action story!