Blue Fantasy: Right off the bat I'm getting Omori vibes with the instrumentation. Pretty track! Love the tempo change towards the end.
Guidance: Very fun and matches the story you gave. Feels like a character theme for Moon similar to Mari's theme from Omori.
Fun In Coral Town!: Groovy town theme. I like how the melody is more upbeat and centered around the major tonic, while the chords indicate minor (I don't think I've heard a V-i movement in a town theme till now!). Gives me a sense of happiness while also holding some mystery and darkness. Unique town theme! Hold up I just read your story description for the track, it lines up perfectly! Great theming! My favorite track on here.
Abyssal Nightmare: Getting spooky. This paints the perfect horror aspect for an Omori inspired OST.
In Loving Memory: Emotional! I particularly love the part after 1:20 with that synth.
I really enjoyed this OST. Great work!