Vital Stats:
Full Real Name: Haku Kaen
Age and Birthday: 19, October 30
Birthplace: Nei clan, Gen village (a country ruled and regulated by Konan country)
Seishi Name: Soi
Seishi Character: The kanji for "Tassel", on her upper left thigh
Seishi Ability: "Hakuujin Raihou," some sort of spell that manipulates electromagnetism (if I'd actually learned anything from 3 years of electronics engineering maybe I could explain this better)...oh, and Bouchuu magic (is that a seishi ability though?)
First Appears in: Episode 27 of the anime
Blood Type: O
Height: 170 cm --> 5'6"
Hair Color: Wine color (mauve-ish?)
Eye Color: Green

Personality:
Soi has had a pretty rough life, so I would say that she's untrusting of others. The devotion and loyalty of the Suzaku seishi to each other and their Miko puzzles her, but at the same time she herself is very devoted to Nakago. I've read that she has a very forceful, masculine way of speaking, but this could be a shield for her more vulnerable side...

Yes, but what can she do?
Well, the ability to throw lighting can come in tremendously handy at times (what, haven't you seen even one episode of Sailor Moon?)...especially when the enemy is out on the ocean somewhere -- ooh, lightning is *very* handy then. What's interesting is that even if Soi fails to destroy the Suzaku seishi, Nakago is very lenient with her and whereas he might not think twice about killing off his own seishi for similar mistakes, he would give Soi another shot at achieving her mission.
Soi gives Nakago little chi power-ups by using her Bouchuu magic (sex) skills to send him her chi. But this spell can also be used to take chi away from a person, and this could be a very effective weapon if used on the right person...

Thoughts:
Soi is definitely a cool character. I like her second only to maybe Amiboshi on the Seiryuu side. That's because I believe Soi is basically a good person; she only does the wicked things out of obedience and devotion to Nakago. You see, he really helped her out in the past and the poor girl's gone and fallen in love with him. So she would do anything, even sell her soul to the Devil, if he asked her to. But she doesn't have anything personal against the Suzaku Seishi or Miaka. She's even been known to help them out a little bit on occasion.
Unfortunately, Nakago doesn't seem to return Soi's feelings (oh! to understand unrequited love! It breaks your heart). She's still willing to sacrifice herself for him anyway. And it turns out that she means more to Nakago than he's been willing to admit in the long run. Who says only Suzaku seishi are devoted?