An extinct branch of Fey, developers of lost (but legendary) music, as well as at least one weapon of terrifying power.
(A black hole. They pretty much invented a way to conjure a black hole. Yikes.)
Fun fact: since they’re all gone, and they lived before See Mab (throne) and Jaden (scepter). (More will come soon once Notte has been released!)... and See Mab (throne) and Jaden (scepter). chose sides, they are technically neither Seelie nor Unseelie.