"Most unfading" implies something that is everlasting, eternal, and timeless. Therefore, antonyms for this phrase would be words that imply transient, temporal, and ephemeral. Some antonyms that come to mind are fleeting, momentary, impermanent, and fading. These words suggest things that are short-lived and will eventually come to an end. Other antonyms for "most unfading" can include vanishing, perishable, temporary, and mortal. These words all suggest that something is limited and subject to the passage of time. Overall, antonyms for "most unfading" suggest that there is an end or limit to the object being described.