first of all the story is very interesting and i'd love to play a game like that, i can clearly hear those inspirations in your tracks :)
drifting to sleep is a very nice calm track, the instruments are great, it makes me feel just like you described it, really reminds me of chrono trigger in a way. and as the track goes on more effects are being played changing from the clock ticking to the sea waves and bubble sound effects. the sound design is on top, great job!
dreams of water really gives that underwater vibes, with fishes and other stuff around. synth work is great there, the structure is very interesting as well, i like the panning rhodes(?) and how full the mix sounds while keeping it simple and some of the effects from the previous track being played here as well trying to keep the style same but at the same time being different and so original. it sure has that adventure-exploring feel to it. again, great job
dancing with the fish spirits is a very interesting track, being so cheerful and at the same time mysterious (cuz those are fishes and theyre ghosts?), i like the mix of electronic, ambient and orchestra bits in it.
mystery also has a nice sound design, sounds mysterious, would definitely fit for some puzzle mini game or something, or also exploring a hidden location in the game.
overall i can't point out which one was my favorite but i can clearly say that the whole ost is my favorite one, it fits so well to the concept, the sound design is amazing as well, great job!