They are monsters who live in the ocean and originally possessed shells, however it is supposed that they abandoned their shells through the process of evolution due to the necessity of showing off their own bodies to males. Aside from crawling along the bottom of the ocean, they can wave the part of their body that flutters to move through the water as if floating. Their bodies are so soft that when touched by another person their hands will sink into it. Likewise, they are a docile race with a soft demeanor and temperament.
Their bodies are adorned with fins, and depending on each individual and the environment in which they live, there are many different beautiful colors and a variety of patterns, which makes them appear just like a lady wearing a dress. Those who behold the elegant figure of them swaying their fins will likely be charmed. The beauty of it enthralls not only men, but women too, and even among humans, dresses that were patterned after their appearance are favored by noblewomen.
The feelers growing from their head sense the presence of men and unconsciously guide them towards them. It's said that occasionally they even come up to the surface. However, they themselves are extremely gentle monsters, and even if they do encounter a man, they just act spaced out or approach him in a calm and friendly manner, and would never aggressively attack. On the other hand, the tentacles that they have on their backs act autonomously from their will and thoughts, and upon sensing something moving behind them, they will automatically seize prey or attack an enemy. If it’s a human man that's there behind them, they will aggressively capture him due to the monsters' instinct, sometimes even coiling around his body, teasing him with pleasure to the point of ejaculation, according to what some say.
They don't have any sensation in the tentacles on their back, but the feelers on their head are sensitive to men's mana, however, since they can only sense the location of a man extremely vaguely, they will just continue to search for a man who isn’t in their field of vision regardless of the fact that they're actually carrying the man on their back. It is often the case that they will finally realize that a man is stuck in the tentacles on their back only after the mana has been squeezed out of him countless times by their tentacles. Thus in the situation of encountering a tritonia, hiding oneself is dangerous, and it's probably safer never to go behind them and instead inform them of your presence from the front.
They have a habit of recognizing things that have sunk into their own body as belonging to them. In the case that a man buries himself in their body, or even if they themselves, to look after him, embrace a man who was violated by their tentacles; in either case they'll recognize the man as their husband and seek to copulate. When having sex, they'll embrace a man to hold him inside their soft body and do it while gluing each others' bodies as closely together as possible. They like to have their husband's body sink inside their own more deeply. Besides just deeper pistoning, such things as deep kissing and burying one's face in their soft breasts are also likely to greatly please them.
Also, it's not just the man's body that they try to make sink inside them. If it's an unmarried individual, she basically won't refuse any man who wants her. And towards the man that became her husband, she'll show a deep tolerance as if she's willing to accept anything. When a man seeks them and begs for their affection, they experience powerful joy as if their husband's heart is sinking inside them and becoming theirs, so they will repeatedly gently embrace and have sex with their husband, continuously providing pleasure and comfort so that he will be dependent on them.
- This monster girl is based on a genus of sea slugs, nudibranchs, shell-less marine gastropod molluscs in the family Tritoniidae.