There's this delicate music box quality running through the entire Shirogane no Torikago soundtrack that perfectly matches the caged-bird imagery. The main theme gets three arrangements and the music box version is honestly the one that sticks with you.
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"囚われの小鳥達" sets up this confined, melancholic tone with light strings and piano, and then "白樺の森" opens everything up with warmer woodwind textures. The shift into "権威の威圧" brings genuine tension. So fragile overall. "飛び立つ" earns its release by the time it arrives, building from the restraint of everything before it.
If atmospheric visual novel scores are your thing, this one rewards patience.