|This article is about the Cardian. For the Sailor Animamate, see Sailor Aluminum Seiren.|
|Lives:||Inside a card owned by Ail and An|
|Occupation:||Servant to Ail and An|
|First Anime Appearance:||The Culture Fest is for Me? Queen Rei Sings With Passion|
|First Manga Appearance:||N/A|
|First PGSM Appearance:||N/A|
|Actors:||Megumi Ogata (anime), Lisa Dalbello (dub)|
She resembled a pink-haired mermaid, and could use her long hair to trap her enemies; once they were incapacitated she could absorb their energy into her hair, making it turn blue, or into her golden scales. She could also shed golden particles from her tail that would make humans fall into a deep sleep when touched by them.
Seiren attacked by firing a stream of water from her mouth at her target. This attack managed to neutralize Sailor Mars' Fire Soul, but proved useless against Fire Soul Bird. This last attack damaged the Cardian's skin, which freed the energy she had previously stolen from the Sailor Senshi and revived them, allowing Sailor Moon to destroy her with Moon Princess Halation.
- Seiren's name is a direct reference to the siren of Greek mythology.
- Seiren could only repeat her name in the original version, but in the English dub she was capable of speech.