Rayek's Sealed Letter is an item in Diablo Immortal. It is received automatically as part of the Terror's Tide update, and required to activated The Chainbreakers.
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Have you seen those red boulders everywhere? One of them landed near the Wolf Gate, and the guards are unbelievably tense. I barely carved off a piece before they chased me away. Now they're clanking around and arguing with people in the street, and my work's even further behind.
I have an awful feeling about all the omens we've been seeing. Would you investigate? Cain asked Commander Kaya to put her seal on this letter. It should help you out.
-Rayek
Let the adventurer pass—alone. They've done a lot of good for our city.
-Kaya