While we know that Aya has a big crush on Mitsuki (mostly rizz version), the reverse is unclear.
Her seduction moves are mostly unconscious and she got close to Aya because she wanted a friend to share music, something she hadn't ever had.
So, I'd think that for now, Mitsuki's feelings aren't romantic in nature, but more like she found a soulmate and a pillar of support for her fragile ego.
When Aya thought she was a boy Mitsuki was actively flirting and knew the implications of their interactions because she got to hear a play by play of it at school afterwards. She had too much info for it to all be unconscious rizz for much of the misunderstanding part. She liked what they had going on. That's why she felt so torn up because she thought what they had would all fall apart to nothing once Aya found out she was a girl and retreated into a friendship request by the end. Even Aya thought that was silly when she heard it. Aya didn't ask for that and has been working her way out ever since.
We are due more info, particularly more Mitsuki POV, but I don't think we're waiting on Mistuki to have romantic feelings start. To me Kanna and Joe who know her best are accepting her relationship with Aya in that way already.