The Ocean Kept Our Secrets conveys night-time with the instrumentation, and takes me back fondly to a lot of the doujin stuff my friends and I have done. Violin came in rather subito; might wanna volume automate that a bit I think. The only connection between the ocean and the music here, is the text, I feel: I feel that the ocean-ness of it all could be communicated more in the instrumentation, e.g. through harp shimmers. The best narrative device is show, don't tell.
What the Night Carried Away already conveys the idea of reminiscing on the past, from the get-go, with the laid-back drums, slow strolling pace, and delayed guitars. That palm muted one feels so good, and I think is what makes this track, keeping up the rhythm of conversation when it (theoretically) happens.
The Weight of Small Things... that opening synth already gives Zelda, entering a dungeon, discovering a treasure chest, but it also brings to mind a musical box, the kind of thing we're inculturated to associate with childhood memories. All in all a very, very fitting track for the discovery of the memory box.
What She Left Behind... it feels heavy. The dissonance not long after the beginning kinda suggests it's a memory that the protag would rather not hold on (which I believe is not the intention here). Is that memory fond? Is the memory something worth holding on to? Is it a hard one? Is it a beautiful summer and the memory is tinged with grief? These are questions for which the instrumentation and compositional choices can provide direct answers.
A Piece of Summer, again beautiful palm muting here. This one conveys what you've written on the text well: a stargazing piece, a nice closing track that leaves some things unresolved (something you communicate well with your chord usage). A track that, with the violins, the mysterious chords (Gm > Abmaj7 > Fmin9 > Abmaj9 > Gm7 etc), conveys the vastness of the sky, and the idea that our protag's friend may be gazing from above. When it gets softer it feels hopeful. I know that wherever you are, you're watching, and I'm not alone, kind of deal.
Overall, this is good soundtrack writing. Well done, and all the best this jam!