That was a close one. Almost didn't read this because the generic looking cover and campy description. Thankfully, I noticed the comedy tag somehow. Funniest thing I've read in quite a while.
Chuunibiyou knows he is chuunibiyou but don't care. Gets reincarnated. Makes up bullshit because he wants to be a cool chuunibiyou. Doesn't know his bullshit is real and doesn't notice he is saving the world. Hilarity ensues.
It’s so good, because it ignores so much. Might be troublesome the later it goes, but at least for now... in the beginning, it’s a great tool for plot convenience and progression.
My interpretation: his isekai cheat skill is that the god in charge of the world supplies his subconscious with real facts whenever he tries to come up with nonsense backstories and whatnot.