Erinyes feather

When Mira and Grokko agree to free the Erinyes Vastren from the Spire of Conjuration, Mira makes sure to include in the contract the receipt of a token of appreciation. Once they complete the ritual and Vastren steps free from her prison of the last few thousand years, she steps directly up to Mira, plucks one of the deep red feathers from her wing, and hands it to Mira, who accepts it and bows.

The feather is uncomfortably hot to the touch without being harmful, like a freshly made cup of coffee. Mira heeds Grokko's warning to hide the feather from Anrel and Vichthart as they likely won't approve of freeing a devil.

Investigating the feather in the 3 days that follow, Mira learns that the feather is not inherantly magical but could have some properties for the purposes of spellcasting. He can't establish a monetary value for it, but in that it is a token that not many people on the material plane can claim ownership of, it is valuably rare.