(Leaving a review here as well, after all this is sort of a honorary entry to the first phase :p)
Mix and sound design / instrumentation are very well done, that much I can tell immediately. Quite interesting choice to mix these glitchy / lo-fi percussions with well-defined acoustic instruments and clean synths, but I think does work well, gives a touch of sci-fi to it. Balance is good, everything has its own place and elements utilize the stereo field well.
I’m not entirely certain if that piano is the best fit to the song however, especially considering that other sounds are a fair bit brighter. Also at some points, such as 3:13 it kind of feels like it could use some additional clarity, because now it sounds like it gets a bit “entangled” on itself.
Structurally everything is in condition. The transitions between sections feel very natural, especially the one at around 1:30 leading into the calm break. That and the latter 2:41 breaks do indeed provide some fine contrast to the rest of the song, which is otherwise quite busy with all the melodies going on.
And speaking of the melodies, those are simply amazing. I don’t think there was a single moment in there where I didn’t vibe with the melodies, especially since they constantly keep evolving ever-so-slightly and get complemented with new selections of instruments.
Theme-wise this also perfectly achieves what it sought out to do, I can perfectly picture a pair of cats making their way through the overgrown ruins of a once great metropolis :) Nails that sense of playful wonder, while retaining bittersweet undertones.
In conclusion, good stuff all around, a true treat for the ears :)