Piano themes are always the most difficult because it’s easy for them to sound cliché, even more so if they are minimal. However, that’s not the case with yours… really well executed, and at some points, it reminded me of the world of Johann Johannsson. Personally, I would have added some background elements (even simple modulated noise) to reinforce the atmosphere and pay more attention to details.
The video where you described the story scene by scene is great; it makes the music more evocative.
Maybe I would have orchestrated the second track differently with some pizzicato, because its writing was very interesting. "Morning Shrine Visit" is one of my favorites: the combination of soft piano and harp is very relaxing, fits well within the overall OST, and is perfect for the type of game you have in mind.
Certainly, extra points for the level of detail with which you described the story and the music, and also for the amount of music you composed (18 minutes is a lot for just one week!). Overall, I think it's a great piece of work.