How Did I, a Dead Apostle, Become Humanity's Last Master?

Humanity is on the verge of collapse, and Gao Ge is freaking out.

But soon, he realizes that he isn't human anymore, so he stops worrying.

That is, until one day, he somehow arrives at Chaldea and becomes the last Master of humanity.

And so, a certain story begins.

(The story's setting differs from the main Type-Moon works. Please don't scrutinize it too closely.)