Seafolk（海人族, Kaijin-zoku / 深海族, Shinkai-zoku) were a race of beings that originated in the sea.
The Seafolk were a violent race of ocean-based creatures with a goal to take the surface of the Earth for their own and make humans their cattle. They were large humanoid creatures that possessed various aquatic animal traits such as gills, tentacles, and fins.
Even the messenger of the Seafolk had a threat level of "Wolf." Combat Seafolk have been shown to be powerful enough to lift a mini-truck with one arm. Several of them together were even more of a threat, with a threat level "Tiger". A group of Seafolk have been shown to be able to push a mid ranking A-Class hero to his limits.
Hero Association Saga
Sea Monster Arc
The first Seafolk rises from the sea and starts to head inland, but before he could even leave the water, he is destroyed by Saitama. Some time later a large wave hits the shore of J-City carrying several Seafolk with it. The Seafolk then rise from the water and begin to wreak havoc in the city. The hero Stinger shows up and saves a citizen from the grip of one of the Seafolk.
The Sisters Who Have Too Many Things Happening
During the Seafolk invasion, a shrimp-like member of the species is backed into a corner by the Blizzard Group, Lily tries to go in for the kill, only for the Seafolk to attack her with Acid Spit. Fubuki appears and disperses the Acid Spit before it can hit Lily and then proceeds to kill the Seafolk.
Webcomic and Manga Differences
In the manga, Seafolk attacked by the shore, in the webcomic it was in the city. 
- (As one is killed by Saitama) "Then, you humans shall live on as our cattl-GROAAAAAAAAAAAAHHHHH..."
- Lord Great White appears in Season 2's opening.
- ↑ 1.0 1.1 One-Punch Man Manga; Chapter 23, page 4
- ↑ One-Punch Man Manga; Chapter 23, page 13
- ↑ One-Punch Man Manga; Chapter 23, page 17
- ↑ One-Punch Man Omake; Sense
- ↑ https://imgur.com/a/HTjEC