The world changes. All cities fuse into a single, infinitely tall tower reaching the heavens, trapping people on their respective floors. The tower has no end, and each floor has a randomly generated environment, where resources and dangers coexist. The corridors are crawling with terrifying mutated creatures. The Sky-Piercing Tower, “Floating City”: a global fusion and an apocalyptic prison.
From the start, he has the worst luck imaginable: he's transported to a “prison” floor with nothing in it, not even a window that hasn't been sealed shut. He has no idea how much time is passing… All around him is despair…
I'm reading it now, the writing is good and quite attractive~