Arcana is officially over, and as such, I checked some details over with Brett and figured I would put up a post explaining as much as possible about !Katie. Yes, I knew who she was this whole time... probably because I designed the character.
I shall start with some of the more common questions:
1. Are !Katie and Souichirou the same person?
A: No.
2. Does !Katie look like Katie all of the time?
A: No.
3. Is !Katie the Page of Swords Reversed?
A: Yes.
4. Just who is !Katie?
A: !Katie is a seventeen year old, Japanese student named Yumeka Kato. She has plain features and longish black hair with bangs. The only thing that stands out are probably her eyes, which are gray. She goes to Shunyo High School, which would be Kyoko and Reiji's school. If the PCs were to meet her on the street, they'd probably think her quiet, shy, and maybe even a little sweet.
Those qualities are, of course, a front. Yumeka is (probably no surprise) a manipulative, petty bitch who genuinely loves spreading misery and misdirection. She's very smart - as smart as Katie - and skilled at acting, breaking and entering, and other nifty things along those lines. Her powers are mind shield and alternate appearance; she can make herself and other willing people look like whoever she wants, with two important exceptions. She can't change eye color, and she can't change gender. Souichirou's gray eyes was a lucky coincidence. She could not, incidentally, keep appearances up indefinitely. Each appearance drains her EP at 5/hour, so eventually they would drop.
Edited in: Greg asked this, and it's a good question. No, Yumeka COULD NOT imitate other people's powers. She also couldn't copy skills or personality traits. Just appearances.
Also edited in: Nic asked this, and it's also a good question. Yumeka's voice changes with her appearance, and so do those who get appearance changes from her.
I remember working out how Yumeka ended up at Shunyo... she lives with her aunt, and if I remember right, she killed off her father while looking like her mother with a few incidental witnesses, so her mother was subsequently sent to jail and Yumeka got to be all "traumatized". I actually had it all worked out and approved by Brett, way back in the day, but I don't have the sheet or log for double confirmation. Oh well. Long story short, she didn't like her parents much (though they never did anything too horrible to her), and she got rid of them. I think they were too nosy. She was subsequently sent to live with her aunt, who left her almost completely alone, which was fine by her.
I'm not entirely sure how she ended up aligning herself with Souichirou, but if he gave her an outlet and sanction for her tendencies, that would have been enough for her. Plus, she gave him a new face - as many faces as he could want. He wouldn't want to get rid of her. Chances are high, though, that Yumeka was the most ruthless in his group. Chances are also high that she would not generally reveal what her real personality was to them as a general rule. Shy and quiet is the default.
She was, in fact, Seiji Usukani's girlfriend (that would be the drugged up biker who Satoshi may or may not have killed). His death, along with the subsequent reading about the Wand, gave her all of the excuse she needed to come up with a plan to infiltrate the PCs, get it approved by Souichirou, and go on to infiltrate the crew while causing as much trouble as she felt she could get away with. It's highly unlikely she cared about Seiji very deeply if much at all - though we can be sure she pretended to. Remember, her primary target was Katie, even before the closet. So yes, she got more glee out of torturing her double than making the boy who killed her boyfriend suffer. It is also highly unlikely that she told Souichirou, or anyone, exactly what she did to Katie. Edit: Though Souichirou did visit, masquerading as Kyon, while Katie was still in the hospital. So he must have had at least some idea.
Yumeka would have been at the battle against the Reversed, since she couldn't wiggle out of it. But who would she have looked like? Who knows. She probably would have been revealed for what she was after death, though, as her false form would have dropped and there are only so many shapechangers in the world.
I hope that clears some things up. This is Arwen the Betrayer, signing out.