Anyway, let's just get it out of the way that I'm rather disappointed with the way everything eventually turns out, even though in some way it strangely fits and is consistent with how the character would have (re)acted.
And let me just comment on the couch thing before going on to other serious matters. So after 20 episodes, the W guys finally figured out that they should fall into a faint on a comfortable couch rather than on a cold hard floor/ground. Philip first did it, taking a few shaky steps back as he fell unconsious onto a couch (and that made me wonder why he hadn't simply stood right in front of the couch (or sat down on it) in the first place and so avoided having to take any step at all). Shou had it better than Philip, since he was already sitting on a couch (at the morning karaoke), so he simply laid down.
So Aya is a police officer newly transferred from Los Angeles. She called Terui 'Ryuu' and he didn't bat an eye. (Her explanation being they all use first names in America and she's used to that. And while it's true that U.S. people are mostly on the first name basis (at least from my limited experience), I'm not sure that they are also being casual like that among police officers...)
But anyway, I was being deceived time and again by her, even after knowing that she was a Dopant. (And that one should not be difficult since everyone kept saying that it was nearly impossible that the guy 'jumping' off a cliff would have survived, and no secret that he was someone Aya looked up to, if not loved, but I think I was too focused, too distracted by Dopant's voice not sounding female...)
Even though I kind of suspected that Aya was lying to Shoutarou by that point, I still cheered for her to choke Saeko anyway. Too bad she didn't. Still, I wasn't really surprised since I got a feeling that she wouldn't.
Luring Terui out by pretending to be the owner of W Memory? Not the most cool thing (probably the only thing she did I strongly disagreed with). I truly had no clue until she sort of confessed it to Shoutarou, as a comment that maybe he and Philip might have to join Terui in death...
Oh well. Not sure if I've explained how I feel well enough. I guess I'm bemoaning the loss of some potential here, not that I can put my finger on exactly what they could do to improve her character. To me, Aya is actually pretty awesome already, and I expect better treatment of her character other than making her mindless with revenge to the point of being consumed. Like Shou (ah, I seem to have same answers as Shou does lately), I really really believed she was above letting destructive emotions control her reactions, that she was strong enough to withstand the power of the GaiaMemory.
But, in the end, even betrayed like this, I think I still prefer Shoutarou to continue to believe the best in people and not be unnecessary cynical, especially since there are already other characters (like Philip...or Terui) who could (and would) inject some reality into him. Because he will be betrayed again and again and again, but I hope even if it's hundreds of time, he won't ever lose that charming naivete, that innocence, and that he will always be willing to give people a fair chance, no matter how unlikely their innocence might be. (And now I think I've mixed up my shows since that last part is very similar to what is said to another character on another show... Oh well, why lie? I've more or less copied it from there.)
And call me oblivious, or something, but I'm not very certain whether Aya has died. I rather think so, however, especially since Terui says something about carrying on her burden. Moreover, I personally don't think she will be very comfortable with living while knowing full well that she has caused dead to others...
ETA: That 'betrayed hundreds time' line doesn't even originate from that series but from an older series. And I wonder why I'm still keeping this a secret anyway since it's probably like saying characters A, B, C but then describing them in a way that leaves no doubt as to where they come from.
ETA 2: So I'm done with being cryptic. The line comes from an older Ultraman series, according to Ultraman Mebius. And, from what honou_no_izumi told me, apparently it has also been used in Kamen Rider series, especially in Kamen Rider Blade.