Ichiokunen Shugyou no Mujikaku Kensei

The only reason he is the strongest is... effort!! Ichitaro, a high school boy, has a personality that causes him to get completely absorbed in a single thing. One day, his entire class is transported to another world as heroes. The hero rank assigned to him at his destination is the worst. Deemed a useless existence, Ichitaro is locked away in a prison where time has stopped. What he did there... was training for 100 million years. By the time he left the prison, he had mastered each and every