It's clear that the narrative of this game is the thing that has been though out the most. It's rich and elaborate, and communicates the dynamic with Nao and the world around them well via the players actions. From an artistic standpoint as well, this game sounds beautiful. Mechanically speaking though, it feels like the players actions don't hold a ton of weight. It really feels like the most interactive part of the game is the walk, rhythm game but the rest just feels like 'here's what happened *because* of this walk.' Outside of that, it doesn't read like there's much of anything else the player can control.
As with others, scope sounds like a big challenge to keep under-wraps. Because of the way you have designed the narrative, there sounds like so many moving parts, and adding several different camera POVs will only create more work. It might prove the project well to really hammer down the rhythm game mechanics first, make sure they're fun and engaging for the player, and then focus on the narrative.