God-Tier Summoner: Summoning a Demon God from the Start

I have zero talent for magic, and the whole school mocks me as “the biggest good-for-nothing in history.” Even the genius girl looks at me with disdain? No matter. One Akashic Grimoire lets me turn around and summon an apocalypse demon god! While everyone else is still congratulating themselves for summoning a single goblin, mythic heroes already stand at my back. “Listen up. From today on, I’m not a good-for-nothing. I’m your god!”