Roar of Ages is a short story by Junji Ito. It is Chapter 3 of Voices in the Dark.
Plot[]
Masaki and Mimura are hiking in the woods when they realize they're lost; their compass and phones won't work. They come across an unexpected flood of water with people trapped and drowning in the current. Masaki and Mimura try to call for help, but still can't get a signal on their phones. It hasn't rained and they have no idea where the water came from. They think a dam must have burst somewhere but, although there are signs of a flood passing through, the ground is completely dry.
The two camp out overnight and try to walk back the following day, but are cut off by a sudden flash flood. Although they get out of the way, others are caught in the flood and drown. Masaki and Mimura realize the people are identical to the ones they saw yesterday. Mimura gets out his camera to film the scene. They walk on and come across a man living in a hut.
He tells them the floods are an illusion. Thirty years previously, he was the only survivor of a village whose people all drowned during a flash flood when a dam burst. Ever since then, the image has repeated itself, and he became obsessed with trying to rescue his wife from the flood, but can't since she and all the other people are ghosts. However, the illusion is becoming hazier and he worries it will soon stop. The man's son had developed a severe phobia of water, and had to be left with other relatives.
Masaki, an orphan with a fear of water, comes to believe that he himself is the man's son. He asks the man what his son's name was, but before the man can answer, the flood comes back. The man once again tries and fails to rescue his wife. This time, he jumps into the water after her and is carried away. Masaki believes the man had spent so long chasing an illusion that he eventually became one. However, Masaki will now never know if he is really the man's son.