A high school student named Ichitaro Yamada possesses a singular characteristic: when he becomes engrossed in something, he does not relent. One day, his entire class is summoned as heroes to a different realm. However, when their hero rankings are disclosed, Ichitaro receives the lowest rank possible. Labeled as ineffective and unnecessary, he is cast into a prison where time has frozen. Rather than surrendering, Ichitaro resolves to do the only thing he can: train. For 100 million years, he hones his body, mind, and swordsmanship, mastering every conceivable style. By the time he finally escapes the prison, the boy who was once derided as the weakest has transformed into an unparalleled sword saint, capable of conquering another world.