400 years before the Order of the Sacred Flame landed on Ovis, the mermaids were at war with the human colonists. They held the belief that, as the children of the ocean, Ovis and its surrounding seas were their birthright. Despite their best efforts, they were steadily losing the war against humans. One of the soldiers, Chloeri, disagreed with the then leader of the mermaids's mentality, that the mermaids should give up on the war and focus on their survival, and lamented how their creator god had abandoned them.
When Chloeri returned after a battle to speak to the leader again she was gone, but a beautiful black spear, the Longicolnis, sat in her place. It drew on the power of lightning and thunder and could pierce metal armor. Chloeri used it to start the war anew, giving the mermaids an advantage.
However, the spear was stolen from the Mermaid Sanctuary by Berevra, Chloeri's sister, and given to Lucius Batraal. Without the spear's power, the mermaids could no longer withstand the attacks, and so Chloeri and the mermaids had no choice but to retreat to the west, where complicated tides, thick forests and swampy land protected them ever since. At some point since then, Chloeri became the official leader of the mermaids, and Berevra remained missing for the following centuries.
By the time the events of The Knight of Lodis take place, the mermaids continued to hide in their sanctuary, mantaining an hostile disposition towards any human who strayed too close to their territory. The human Alphonse Loeher, who wished to speak with the leader of the mermaids, encountered Minerva and followed her to the shores of Rana where he was met with a squad of soldiers led by Aerial. Once the battle was over, he was granted audience with the mermaid leader, Chloeri, who explained the story of the mermaids of Ovis to him and that of the black spear. She also told him to tell Berevra that she and the others had forgiven her, and that she was welcome home again. Before he departed, Aerial offered her services as a soldier, but also warned him that any act of betrayal towards the mermaids would be met with her spear on his back.
Alphonse returned later to tell Chloeri that he had seen her sister and gave her the message. Chloeri held out hope in the belief that she would see her sister again and gave Alphonse Zephyrus.
Some time after the defeat of Shaher, Chloeri passed on to heaven with the spirit of her sister, and Aerial took command of the mermaids in her stead, with an understanding that there were humans that she could trust, and passed that knowledge unto her followers.
- Chloeri - Leader of the mermaids during the events of The Knight of Lodis. Passed on after the defeat of Shaher.
- Berevra - Sister of Chloeri. Fell in love with Lucius Batraal and gave him the Longicolnis, then took it back after his death. She also rescued the infant Eleanor Olato and watched over her for ten years. Passed on after the defeat of Shaher.
- Aerial - Mermaid soldier. She battled against Alphonse on the shores of Rana, and later joined him (Minerva alive) or not (Minerva killed). She became the leader of the mermaids after Chloeri's passing.
- Minerva - Sister of Aerial and a mermaid soldier. She encountered Alphonse on his way to Rana and either was rescued by him (Path A) or fought against him (Path B).