The Demon King Overrun by Heroes

I followed the ‘Demon King’s Playbook’ to the letter, only to be killed by the Heroes. You’re telling me my Tower and I were just a custom-made grinding spot for them? Now that I’ve regressed and got a second chance at life, to hell with that shitty Playbook—feed it to the orcs! The survival story of Berge, the wacko(?) Demon King!