It's the story of Re:zero except Subaru Natsuki has Sans Undertale power's. He will follow a similar story line with a few changes ;).
Another rat. ...... Ah, but those eyes... a starving wolf. Before I kill you, tell me your name. Tell me your name! ...... No name to give? You shinobi are all the same. …
In this world, demons, devils, and all sorts of other monsters are real and some walk amongst mortals. A man keeps watch on all of this. A Spider-Man.