Im Quitting Heroing GN Vol 02

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?