In Lludd and Llefelys, the Coraniaid arrive during the reign of Lludd, son of Beli Mawr, and become the first of three extraordinary afflictions troubling Britain. The tale does not need them to win a conventional battle. Their advantage is information. It says that no discourse on the face of the island, however quietly spoken, remains unknown to them if the wind meets it. That ability prevents Lludd's people from planning an attack without revealing the plan at the same time.

Lludd therefore seeks help from his brother Llefelys, king of France in the story. The brothers meet at sea and decide that even their private conversation must be protected from the wind. Llefelys has a long bronze horn made so they can speak through it, but a demon inside the horn turns their words into hostile speech. Wine is poured through the horn and drives the interference away, allowing Llefelys to explain the Coraniaid's weakness.

Llefelys gives Lludd special insects and tells him to keep some alive in case the danger returns. The rest are to be crushed in water. Lludd must then call his own people and the Coraniaid to one gathering under the pretence of making peace and cast the prepared water over everyone. The tale says the mixture will kill the Coraniaid without harming the Britons.

Lludd follows the instructions. The two peoples gather, the water is scattered over them and the Coraniaid are destroyed while Lludd's own people remain unharmed. The surviving narrative does not say that the liquid enters their mouths or nostrils, and it does not explain the insects biologically. They are simply the magical means by which Llefelys solves a supernatural problem.

The Coraniaid also appear in Welsh Triad 36 as the first of the Three Oppressions that came to the island and did not return. The earliest surviving triadic text places them in the time of Caswallon son of Beli rather than Lludd and says they came from Arabia. Later textual discussion connects the triad with Lludd and Llefelys. This variation matters because it shows that the Coraniaid tradition moved between different medieval historical frameworks.

Modern scholars have proposed several explanations for the Coraniaid's name and identity, including possible confusion with the Cesariaid or Romans and other attempts to relate them to foreign peoples known to medieval Wales. None of those proposals has become a secure historical identification. For Mythopouch, the safest treatment is the one the medieval story itself supports: the Coraniaid are a legendary invading people whose impossible hearing turns secrecy into the central problem of the first plague.