I'm a Self-Proclaimed Agent of God: Everything Will Be as Shown to Me by That Person... I Kept Saying This, and Now I Can't Back Down.

Zero, a young nobleman reincarnated from Japan, finds himself in a world of swords and magic. As a former otaku, his blood starts boiling—he wants to do something chuunibyou-esque! When he discovers his father’s embarrassing "Notebook of the World's Truths" in the study, Zero seizes the chance to roleplay. Declaring himself the Emissary of the Holy God, he begins a grand rebellion against the false gods.