Prologue: Great idea including the main character’s theme in a prologue! I want to use that in the future. Love the dorian vamp with the simple, but memorable and beautiful flute melody.
Subaquatic Saunter: Oh I love your reasoning behind the 5/4, and itt works so well! Rather than even steps like running, swimming sometimes has a long stroke followed by a short stroke. This is peak musical imagery and gets extra points for correlation to theme and creativity from me for this!
Subaquatic Saunter (Action): Good job executing some dynamic soundtrack elements. Electric guitar is a great way to elevate the energy of a track for sure.
Within a Bubble: The jazzy harmony is melt-in-your mouth sweet! I get Pilotwings vibes from this.
Mechacanthine Foreboding: Uh oh, here comes the phrygian dominant. I think it’s always really fun to hear that scale used outside of the context of desert music.
Mechacanthine Chaos: The breakbeat does add to the chaos and makes this feel like a boss theme. A mechanized coelacanth is really fun to imagine as the boss for this tune. I am imagining the scene as being like a chase type of boss fight where the boss is in front of you and you have to swim after it while it knocks boulders onto you and does other things to cause damage. I imagine the sun or some other light source on the opposite side of the giant boss so it looks all shadowy with dust falling from its scales. Fun imagery in your music!
Within the Soul: A nice somber end to this OST. The harmonies took me in a different direction than I expected which helped me understand what the main character was feeling better.
Overall: I appreciate the light-hearted story with the darker mood as you went on, paralleling Sana’s journey deeper into the sea. I love your organization and flow of tracks and your use of leitmotif in particular with Sana’s theme was great! Well done and thank you for sharing!