The world as we knew it has sunken beneath a large body of ocean water, as sea creatures and aquatic monsters from the other side then comes on over through the portals, located around the world.
Earth has become entirely submerged in water, thereby making it the perfect habitat for oceanic life and sea creatures to prosper.
How will our main protagonist Arthur survive by being reincarnated as a deep-sea Angler Fish?

Additional Information:

I was given permission by the author to post the story here on Royalroad.

For the original novel. You can read it here by clicking upon the link below.

Regarding That Time I Was Reincarnated As A Deep Sea Angler Fish. It Was Terrifying.