The Debt of Air: Non-flying immigrants who arrive at the capital cities from the lower valleys must pay an exorbitant "Air Tax" for the right to breathe the clean, filtered air of the peaks. Those who cannot afford the tax are forced into generational indentured servitude to the state.
The Sentence of Dissonance: Criminal Sirin who commit high treason or sabotage acoustic architecture are subjected to The Great Clip. Their wings are ritually severed, their vocal cords are chemically scarred with acidic ash, and they are cast down into the Unvoiced class as the ultimate humiliation.