Mermaid Servants/Synopsis

The Little Mermaid Arc
The Mermaid Servants appear before Nene trying to recruit her to the their side as per the orders of the Mermaid and led by the Pufferfish. The Pufferfish tries to persuade her under the pretense that she will attain high status as a fish and be treated as a princess with the ability to sway many men.

To further motivate her, the Pufferfish reveals he has observed her and Hanako for awhile and assesses that Hanako treats her poorly, and unfitting of her. He further elaborates that contrary to appearances, the Mermaid is actually kind to her people, and that Nene will be treated well under her care. He gifts Nene a vial of Mermaid Blood for her to drink, explaining that it will sever her bond with Hanako and give her the benefit of no longer transforming when in contact with water. The fish promise to return the next day.

After seeking counsel with Tsuchigomori, Nene decides against drinking the vial as she still believes her bond with Hanako to be true and tells the fish of her decision. To further convince her, the Pufferfish shows scrolls with portrayals of all the possible marriage partners for Nene to choose from, all of them male Fish. As she's dragged by the Fish into the pond, Nene realizes all too late that she was conned on their promises as they meant she would no longer suffer transformation mishaps as a fish, and that she would enjoy a love life as a fish.

Although confused the Pufferfish seemingly putting Nene in trance, describes all the poor decisions Nene has made, her lack of appeal and her terrible taste in males, bluntly pointing out she is an absolute failure at love. The words leave Nene speechless as she's unable to refute the claims. As an extra layer of motivation, the Pufferfish promises that should she become a fish, she would be at the top of their world's hierarchy for she's deemed a princess by their standards. Tempted by the idea of being a loved girl, Nene almost drinks the Mermaid Blood but is swiftly rescued by Hanako who drags her out of the pond through a net. He soon catches her and restores her to normalcy, while stating that how harsh her current conditions are for her as a human, or whatever sweet promises await her in the Fish world is all irrelevant, for she likes him.

The Pufferfish is angry at his interference and demands that he unhands Nene. Hanako asks them if they weren't taught to don't meddle with other people's possessions and tells them to leave, threatening to turn them into sashimi while holding his knife and showing a paper with a graphical depiction of how he plans to cook them. This immediately terrifies the Pufferfish alumni, as he is left with his confidant cursing Hanako for ruining his plans. Vowing to return, the two fish make a quick retreat.

The Pufferfish and his assistant appear in a pond in the Broadcasting Club, spying on Tsukasa. Having seen that Hanako was mortified at the sight of Tsukasa, they thought they could enlist his help to deal with Hanako to retrieve Nene, but the Pufferfish wondered why the two apparitions looked alike. He was spotted by Natsuhiko and held by him, as the Pufferfish demanded to be released. Sakura told him to release the fish but Tsukasa took it. Having seen the fish beforehand, and under a childish fit of euphoria, Tsukasa wanted to dissect the Pufferfish to see what the insides of a talking fish were like. Despite Sakura's protests, the Pufferfish was brutalized to his death by Tsukasa with a pen as he wanted "to take a peek".

Aftermath
The assistant reported the incident to the Mermaid as a funeral was held on the Pufferfish's honor. The Mermaid was terrified at the idea of an apparition spreading rumors that could meddle with other apparitions. She reveals that although she believes Nene to be unintelligent that she was technically part of them, and thus desired to grant her protection, but that as things were like, that it was best to leave her.