Every person on Hawiyalatari touches the Veil once a night. That's what dreams are — the membrane going thin while you sleep, the rules relaxing, something on the far side pressing close enough to whisper.
The Veil is the realm beyond the world's edge: formless, lawless, older than physics. The Veilkin live in it. The world is sealed against it — sailors who go far enough in any direction find the place where the sky comes down to meet the sea, warm and shimmering and absolutely closed.
A sealed world is a protected world. Fine. But every seal has two sides — and nobody alive knows whether the ones who built it were keeping something out. Or keeping something in.