After Sailor IronMouse (known as Nezu Chuuko in her human
guise) was killed by Galaxia, Sailor AluminumSiren came over to take her place.
Sailor LeadCrow was her rival at first, but 
later the two seem to developed a rather nice
friendship. LeadCrow is also, by the way, Siren's teacher. Siren drives
LeadCrow into fits of anger sometimes because of her weird tendency of eating when she
gets nervous or when something disappointing or wrong happens and usually complains and
laments about things. And she even keeps a diary!
Unlike the other Sailormoon villainess, Siren is extremely polite. Some examples are when the time she takes out her namecard and introduces herself to Sailormoon, she bows (that's something really vital in the Japanese culture, good courtesy...) and uses formal Japanese. Another example is when Siren attacks Eternal Sailormoon and attempts to pull out her starseed she says "anata no starseed wa dashite kudasai" which translates into "please give me your starseed". Now that's good manners :)
Siren has a cute personality on the whole and she is arguably very attractive in her own way. She seems to like sea-associated accessories like the fishey-cloth she uses to wrap her bento box and seashell choker she wears on her neck as Sailor AluminumSiren.
Siren, like the anima mates have no
transformation like the good senshi we know. Instead she just throws up her clothing
and lookie!
She's already wearing her fuku! It's not that she wears her fuku underneath her clothes, probably just some nifty trick villains know.
Sadly, Galaxia killed off Siren by removing her bracelets because of too many failures. Siren did manage to find out the identities of the inner senshi and Sailor Starlights, but she died before she she could tell Galaxia (that's the exact same fate Jedeite encountered! He was murdered before he could tell Queen Beryl who the senshi were.)
In the manga, Siren was said to have came from the Planet Mermaid,
she took the original Sailor Mermaid's Sailor Crystal and made herself a senshi (according
to the Starlights). She only appeared for 7 pages before she was killed by Sailor
StarFighter's Star Serious Laser(talk about under-rated!). She first appeared in the
3 Light's concert and we see her sitting among the audience with this evil smirk and
swirls surrounding her face. In these 7 pages absolutely nothing on her character
was revealed to us although. She also managed to kill Sailormercuty and
Sailorjupiter, and obtained their Star Seeds before she perished. Also, in these 7
little pages Siren has been revealed to be attracted to music. When Seiya was
standing on the school roof singing with Usagi next to him, Siren suddenly appeared, most
conclude that she gets attracted to singing. Like Mistress 9, she could use her long
hair to strangle her victims. The anime would have been a much bit more interesting
if they had followed the manga's storyline more closely.