Merfolk (feminine Mermaids) are a species of half-human half-aquatic creature hybrids native to the oceans of Japan. Sun Seto, the deuteragonist of the series, is a mermaid.
Biology[]
Merfolk come in many different types and forms. Females of the species typically resemble the western depiction of mermaids as being human from the waists up and having fish tails in place of legs. However, males of the species resemble either human-aquatic animal hybrids (the Elite), or fully resemble the animal (Shark). Though, there are exceptions, such as Saturn who resembles a human woman with seaweed for hair (being a seaweed creature), as well as the sisters Maki and Fuki who resemble tiny humans due to being part hermit crab. Some merfolk seem to be unable to take human forms at all (such as Octopus).
Known forms that a Merfolk can take besides the typical western version include: octopus’, sharks, killer whales, hermit crabs, catfish, seaweed creatures, sea dragons,barracuda’s, and even a spectral-like fish.
Merfolk are natural swimmers. They are capable of breathing under water and surviving at the depths of the ocean with no ill effect. When a mermaid dries their body they are able to take human form, however they may revert to mermaid form when exposed to water. Though, adult mermaids have more control over this and can maintain their human forms in water or take their mermaid forms on land at will.
Female mermaids are shown to possess voice-based abilities. The most common ability is a sonic scream, capable of breaking through a wall. They can also learn “songs” that have magical abilities. Suns ability is “Song of the Heroes” which empowers the person of her choosing to have superior strength and fighting skills. With a strong enough connection, the person can draw power from her, just by being around her without the song. Lunars ability is the “Song of War” which was taught to her by her mother as a child. It makes anyone who hears it willing to fight. Maruko has a special ability to cancel out other mermaids voices with her own.
Seaweed creatures such as Saturn are able to use their hair to stick on walls and capture objects.
Lunar's father, an unknown type of sea creature (though given the honorific “tiger”), inexplicably has the ability to shoot devastating lasers from his eyes.
Sea dragons are the strongest-known merfolk. They possess great size, strength, and durability in their natural forms and appear to be even stronger than “normal” sea dragons. Even Nagasumi, empowered by the Song of Heroes, was no match for Gozaburo in his true form. According to Terra, if all of humanity and their nuclear weapons fought Gozaburo (a “true” sea dragon) one-on-one they would lose.
Culture[]
Merfolk prefer to keep their existence secret from humans. It is law that if a human sees a Merfolk's true form, either the human or the Merfolk must die (likely either as a way to keep more humans from finding out and/or to punish the mermaid for being seen). The only exception would be if they, or a relative of theirs (as shown with Nagasumi’s parents) marry the mermaid therefore becoming family. Though under special conditions, the mermaid government can grant special privileges to the human (as shown when Akeno offered this to Nagasumi, although this was part of a mermaid nobles plot to break them up). There exists “Mermaid Inspectors” which enforce this rule and make sure that mermaids living among humans can keep up the masquerade, deporting them back to the ocean if they can’t. In the final arc, it is also suggested that the law can be averted if the human forgets ever seeing a merfolk.
According to Sun, Merfolk value honor and chivalry. Although most of the mermaids shown in the series have been insane, violent, hypocritical, and selfish (although this may be because most of the ones shown have been yakuza).
Despite their aquatic nature, most Merfolk take human or atleast humanoid form. They live in underwater homes, although they are dry and contain air. Presumably for conveniences such as drinking fluids and usage of technology. Many of them also live among humans, such as Lunar who used her voice to be one a famous idol, the Seto and Edomae clans who have businesses on land, and the Mikawa family (the richest family in Japan).
Most Merfolk have names related to bays/seas/bodies of water where they are presumably from: Seto, Edomae, Mikawa, Nakajima, Okhotsk, Sagami, etc. Although there are exceptions: Shiranui (an optical phenomenon that occurs in the Gulf of Shimabara, Japan, around February 24 and September 30) and Fujishiro.
Members of the mermaid nobility such as Yoshiou keep giant eels (anime) or sea dragons (manga) as pets.
Government[]
Mermaids seem to have a government structure that mirrors old Japan. They have nobility members with names such as Minamoto (a surname given to nobility related to the royal family) and Taira. Both of which were the names of noble human families to the emperor of Japan. It is also implied that various members of the human Japanese political structure are actually Merfolk in disguise (which could also mean that previous mermaid emperors/noble houses were kin to the mermaids), as Terra claimed that Rens grandfather recently retired from being the great general of Japan. Therefor, it could be possible that mermaids try to stay hidden from humans for this reason.
The mermaid nobility is close with Terra, the goddess of the world, who is a member of their court. It is possible for this reason that Terra may have had a more direct role in the creation of the mermaids (though she claims to be the source of all life on the planet).
Technology and Magic[]
Merfolk have access to a number of different magical artifacts and technologies. Beyond human appliances.
The Spear of Neptune: A spear held by Rens family (or sold online by the Seto Group in the anime) which has purifying properties. It can remove abnormalities from a persons body to undo magical transformations. It can also purify a persons heart of darkness, turning them good. And even heal a body of injuries. The weight of the spear and ability to be thrown is also depended on the users determination. Sun thought it was heavy at first but was able to throw it at giant-Nagasumi’s head (to the moon in the anime) when she was determined to change him back to normal.
Mermaid Mineral Water: Mineral water that mermaids drink. However, it has an adverse effect on humans. Namely, making them grow to giant size and rendering them mindless. In the anime, it seems to make them able to survive on the moon as well.
Mermaid Exercise Equipment: Mermaids have a water-fall like device that they can work out with by swimming upwards.
Mermaid Love Potion: A potion that causes any man that drinks it to be seen by every woman around them (even relatives) as their ideal man for 24 hours. Though the drinker doesn’t actually change physically, any woman who looks at them will see and hear whatever will make them desire the man most. However, it has the opposite effect on men, causing them to see and hear whatever will make them hate the drinker most, even to murderous levels.
Mermaid Transformation Conch: A conch that causes humans to take mermaid form. For men (such as Nagasumi) it turns them into grotesque fish-like creatures. For women (Mawari) it gives them mermaid fish-tails instead of legs. Unlike regular mermaids, they have these features even on land so long as they are holding the conch.
Akeno’s Sword: Akeno’s Sword generates energy, allowing it to cut through anything.
Fog: Merfolk nobles have access to a special fog that can erase human memory as soon as they are no longer exposed to it. This allowing mermaids to interact with humans and have them forget it later to comply with mermaid law.
Gender-X: A weapon that reverses a persons gender.