Just some pages where how they act may be relevant. I'm writing this down for easier access once there are more chapters and I want to revisit those scenes.
Erika:
School girl usual romance talk, pages 12-13
Tanabata day memories conversation, pages 27-30
Her opinion on how Koto should act about being reunited with Aya, pages 08-11
It's not clear what she means by fair in this, pages 30-31
Self-deprecation? Page 07
Briefly mentions how Koto "has changed", pages 17-18
Calling herself awful, pages 24-25
"What do you think? Aya.", pages 17-18
Recognizing herself as Aya's stand-in, pages 25-28
In the same chapter, pages 29-30, tanabata is brought up again and her wish is shown.
Still within chapter 8, "I consider myself an awful jerk" pages 35-36
Flashback from briefly after Aya's disappearance, makes a question Koto seems a bit confused about, page 11
"I'm not... Anyone's great friend.", pages 20-24
Her animosity towards Aya becomes more noticeable and so does the fact that she's hiding something, pages 09-13, Aya briefly recalls something and Erika's muttering seemed to be directed at herself.
Later, "meaningfully" smiles towards Aya, page 22
Koto:
Second confession, already showing her desire to be the center of Aya's attention, pages 28-31
"I just knew she would respond that way" script and stage, which could mean nothing, pages 32-36
Anxious over Aya's sleeping figure, pages 24-29
Anxious over Aya seeking for a job, pages 31-33
Watching Aya leave for work, page 32
Her wish for Aya to quit leaks a bit, pages 07-12
and in the same chapter, gets somewhat more intense, pages 19-25, as Aya talks about how she wants to keep moving forward
gets more anxious when Aya starts to focus on achieving her goals, pages 35-36
"I would never let go of Aya-chan", pages 31-36
Loses her cool, pages 01-05
and then feels betrayed pages 17-18
Lastly, the part where her emotions leak and she tries to control Aya's actions, pages 25-36 and makes it clear that she is a child and that she is scared of Aya disappearing again.
Aya:
The "If not here, where is it?" scene, pages 18-25, Koto feels as if she's being messed with.
still during the first chapter, she's found looking somewhere far away, pages 28-30
Can't recall what happened and feels insecure about how the current Koto feels about her, pages 27-34
Her reaction to her grandfather's death, pages 01-02
Her reaction when Koto first confessed, pages 01-02
During their date, reminisces on how her feelings for Koto changed since her first confession, pages 10-15 and is now more aware of how she is attracted to her.
Still within the same chapter, her fear of being abandoned becomes apparent, 18-28, at this point she's still very naive and unaware of her partner's mental state or what it means to have disappeared for 7 years.
Becomes lost in thought again, looking somewhere far away. pages 05-07
This entire part where she isn't certain of her standing with the other two, pages 19-36
Feeling bad again for being the only one left behind and a child, pages 23-35
Anxious over a possible break up, pages 02-05
Feeling anxious over Koto, pages 15-30, and getting very awkward after and "comfortable".
During Koto's emotional moment, pages 27-33 her being a child and her disappearance are the two things she seems to be the most sensitive about. In this I'd say her desire for not being "stuck" is made clear.
And she does want to be independent, pages 07-09
Starts to question how she feels towards the current Koto, pages 16-17
And finally starts to become aware of the gravity of her situation, pages 28-36
WOW!!! Thank you for sharing this. it's incredibly useful and helpful! :D