Sailor Aluminum Seiren ( )
The Anime Story
She appeared alongside of Lead Crow after the demise of Iron Mouse. Aluminum Seiren traveled under the disguise of Aya Reiko when she went to Earth. Always by her side to watch over her was her rival, Lead Crow. Lead Crow was always pushing her not-agressive-enough rival forward to do her best. Aluminum Seiren seemed to always come up empty handed when searching for Star Seeds. Galaxia finally decided that she had failed once too often. Before the Animamate could reveal Sailor Moon's true identity to her master she was killed and Lead Crow was left alone.
The Manga Story
She killed the Sailor Soldier of her home planet Mermaid, Sailor Mermaid. When she appeared in the manga she, like the other Animamates, was searching for the Sailor Crystals. She managed to killed Mercury and Jupiter in battle. It was Starfighter who finally killed this Animamate.
Aluminum Siren was the complete opposite of her 'rival' Lead Crow. She hardly ever showed an agressive nature. She would eat when she became nervous and was often very ditzy.
In Greek mythology, the Sirens are creatures with the head of a female and the body of a bird. They were regarded as the daughters of Phorcys, or the storm god Achelous. According to Ovid, they were nymphs and the play-mates of Persephone. They were present when she was abducted and, because they did not interfere, Demeter changed them into birds with female faces (Ovid V, 551).
The idea of mermaids and mermen, the male equivalent, could be based on creatures from Greek and Babylonian mythology: Sirens and Tritons of the Greeks, and the fish gods, who were half human and half fish, from the Babylonians.
Sailor Mermaid, while only mentioned in the manga and never show still exisited so it was only proper that I put her mythology here. Her star seed was stolen by Sailor Aluminum Siren. In the anime, when Siren wrote a note to Sailormoon she drew a mermaid version of her self as the signature. Mermaids and Siren were similar in mythology which would be the reason behind Siren being the one who took Mermaid's sailor crystal.
Seastars & Sailor Tales | The Sailor Aluminum Siren Place To Be | The Slippery Mermaid