Ring depicting a leaden full moon. Symbolic of a cold oath, the ring is supposed to be given by Lunar Princess Ranni to her consort. Ranni is an Empyrean, meaning her consort would by rights earn the title of lord. A warning is engraved within;. Whoever thou mayest be, take not the ring from this place, the solitude beyond the night is better mine alone.

Found in a locked chest next to the Raya Lucaria Grand LibraryGrace Site of Grace - which is available after you defeat Rennala. Unlocked using the Discarded Palace Key.