I really loved this! The sound design and backgrounds in general worked really well to accent scenes. I loved Reisen's vibes and style in particular, absolutely *immaculate*. I really liked the way Kana and Kotohime's dynamic was written (and also, as someone who's grayromantic myself, the representation feels very nice). A small thing, but I do like the way it was split into parts, with each part having a notably different focus; I think that helped to keep the transition from feeling jarring.
The one thing I want to comment on is that Mokou's change of heart felt a tad sudden to me? I don't mind it per se, and I feel like the way that entire exchange was implemented and written still made it a really effective moment. It's moreso just that Mokou's previous conversation and the way she seemed to talk about Keine in particular gave me the impression that she might need some more time to think about and understand her own feelings.
Also, would it be feasible to release the surprise bullet hell section as a standalone thing, or to provide an easy way to replay that specific section? I'm nowhere near good enough to actually do well in them, frankly, but they still seem like they could be a fun thing to try and get better at.