I'm Quitting Heroing, Vol. 2

Leo, the strongest hero, is reemployed in the Demon Queen-s tattered army! Just as he is about to begin the reconstruction, two of the Four Generals go AWOL! It-s time for Leo to put his accumulated knowledge and martial prowess to work and bring about some real innovation, which amounts to...millennias- worth of experience?! What is the secret of the mightiest champion?