Rikuo

Anything bold and centred is official data, unedited even to correct the numerous grammatical issues. Anything else is my interpretation or headcanon.

Social Structure
Rikuo's kingdom is different from a Monarchic Government or Imperical Rule. There are no royal families. Each king is chosen by the previous king. After obtaining the people's consent, the next king is chosen. Every Merman is given a rank, they are strongly united, and they keep a mutual trust with this.
The ranks do not mean a social position but it is more used to give each one a job that suits them: those who gather food, those who protect their own from danger, those who create habitats, those who care's for the young. Out of these many jobs, raising the young is usually done by the males. Similarly, the females are raised by their own mothers.

In the case of males, their mimicking abilities is usually used to scale their strength level. It is important for those caring for the young to teach the young this Rikuo had cleared this ability beyond anyone else. It can be said that, for his son Ricky, he is the greatest teacher.

In other words, Rikuo was not made the emperor of merfolk by birth, but due to his personal virtues and his mimicking abilities which are second to none. I believe merfolk society has no gender inequality; everything is decided based on the individual.
Whilst in Darkstalkers the sasquatch race are well known and have good relations with humans, merfolk are more likely a mystery to other races and vice versa. They lived in seclusion in Atlantis, situated in an unexplored area of the Amazon Basin prior to the mass extinction event which rendered Rikuo one of very few survivors (most likely one of two of Atlantis). However, Merfolk were originally more widely spread as an unrelated family is later found to have been secluded in an area of the ocean for centuries.

Reproduction
The merman race have reproductive periods. The average time for Merman's to lay eggs is around the human age of 16 to 22. They bear eggs two times within one year averaging about 10 to 20 eggs. On average, a couple lays 60 to 120 eggs. But only 10% of these hatch and out of those, only 2 to 5 % of these survive. A few hundred years ago, the lake they used to live in was fresh water. But within the last 10 or so years, sea water had flowed in and caused the salt level to rise. This may have been the reason why Rikuo and his family could live in the sea without much trouble against the salt level. But this may also be the reason for the decreasing birth rate.

This means that males can continue reproducing after a female of the same age. This is canon, as Rikuo is fifty-three years old at the start of Darkstalkers, and has several children with a younger wife.

Physiology
It is important to note that merfolk are not actually fish, and although they are amphibious they are not amphibians (in the taxonomic sense) nor are they mammals despite possessing mammalian features. Attempting to classify them by already existing classifications is a fallacy. Instead, they are unique creatures possessing traits from across the animal kingdom. Further complicating matters is their ability to alter their own physical make up to imitate aquatic races that fit into various identities, including fish, molluscs, aquatic mammals and amphibians. However, they are primarily aquatic and will spend the vast majority of their life submerged. They do require moisture to survive, but in humid conditions such as the Brazilian rainforest, they'll be fine for days. In less moist environments, depending on the temperature, they will require more substantial sources of water. However, thanks to their ability to control water it is relatively simple to find ways to keep damp. This is particularly true of Rikuo who can summon tidal waves in such arid places as Egypt, Mexico and Las Vegas. The moisture does not have to be water; Rikuo has noted that blood works just as well.

All male merfolk possess the ability to alter their form to mimic other aquatic life, however, Rikuo is not a good example to gauge their abilities as his mimicry abilities are prodigious. It is unknown if females are also capable. Rikuo is so exceptional that he can even take on a completely different shape altogether (specifically a giant frog, one of his fight intro poses). Whilst originally a freshwater species, they can easily adapt to live in salt water too. They may also possess the ability to command other sea life, or this could be unique to Rikuo, who rides a Mach Crab and can even control water plants (in the form of creating lily pads usually). Essentially in Rikuo's case, if an aquatic creature is capable of it, assume he is also able to perform that action. However, these abilities are often exaggerated e.g by transforming into a clam shape he can rapidly create pearls and then fire them as projectiles. How this is achieved is unknown. Equally unknown is how they control water.

Merfolk, or at least the males, appear to have very long life spans. Rikuo, despite having a youthful appearance and being in his physical prime is over fifty years old. This is perhaps a reference to his inspiration, the Creature from the Black Lagoon's gill-man, who was possibly millions of years old. It seems that their malleable bodies are capable of rejuvenating themselves, similarly to a number of aquatic species- Rikuo can survive being cut in half for example. In general, they are hardier and stronger than humans, but Rikuo is again so far above the average it's hard to tell how much by using him as an example.