I really don't understand the deep admiration you people have for Erika. She is kind of creepy in my book. I mean move on. Koto has not even once looked in your direction. At least Koto tried, unsuccessfully, to move on and meet new people.
She only wished Aya back so that she can finally get, what she considers her birthright apparently, Koto. She has been completely indifferent to Aya. She was not happy she was back. She was only happy that Koto will finally get her closure so that she can get her obsession. Who is not even remotely interested in her. Get a life Erika.
I mean your childhood friend returns after 7 years. She is scared and lost. But your only thought is that now you can finally get Koto. That makes Erika self-centered to the extreme. Her love is more akin to an obsession. It has been 7 years Erika. Move on. At least Koto and Aya had something going on once.
But really no one really cares about Aya. Even Koto is acting all weird for someone who supposedly believes that Aya was her great love. Her soulmate. Or something like that.
Honestly... Erika reads to me like someone who's erroneously assessing her own motives out of at least a degree of self-deprecation. She very much could have gone out with Koto if she wanted to, but realized that it wouldn't be healthy for her or Koto. She does want Koto and Aya to break up, but as things are now, that's a significantly more justified perspective, but since she also is still attracted to Koto, she misconstrues that motive to primarily be out of a desire to get together with her. Y'know what I mean?