Kapitel 128: Charon - The Ferryman

Souls that die would have to pay the ferryman Charon a gold coin to have him take them to the other side, but if you don't have a gold coin then Charon will refuse to take you to the other side and you will have to swim across the river to get there.

Apparently, swimming across the river takes almost a hundred years longer than it would take for you to just use the boat, and you can get lost in that river for years trying to swim to the other side. It was some sort of deal between Charon and the goddess Styx that allowed him to cross the river in a shorter time than anyone else.