Requirement: a Relic OR one book of deep study of a Relic
Backgrounds: Scholar (practical robes, 1d4 scrolls of lore. Your relic is probably an Orb), Priest (Impractical Robes, Opinions. Your relic is probably an actual relic), Treasure Hunter (Tunic, trousers, ten foot pole. Your relic is probably a magic item)
Each level of Relic-Seeker beyond the first gives you +1 magic dice
You possess some fragment or leaving of a Legendary Power. Determine that legendary power and the relic you possess when you take this class. Perhaps it is a rock cut by Excalibur, an idol of a god, a saint’s teeth, a sea-worn stone, etc. While you possess your relic, you have +1 MD* and can cast 2 spells relating to it (negotiated with the DM). If you collect additional relics relating to either the Legendary Power or something of its kind, you get 1 spell from them.
Lore and Speech
When you come across a thing of the same general class as your Legendary Power (a sword for Excalibur, a knight or king for Arthur, a god for Anu, etc.), you can ask one question about it and know the answer, and you know the proper etiquette, rituals, and language to converse with it properly.
You may take 1 damage commune with your relic and receive cryptic visions related to it. You might receive information about the whereabouts and doings of your Legendary Power, hints as to the locations of more relics, warnings about the past or future, or any other prophetic shit. May not be useful or comprehensible.
Power against Power
You may use MD to invoke your Legendary Power against an enemy. If the enemy fails a save, they are put into enchanted sleep/death/magically imprisoned/banished/etc. The number of MD spent determines the difficulty of the requirement to rescue them (negotiated with the DM). A creature encountering their body/prison (or you, if their body is not present) knows subconsciously their nature and the nature of their binding.
You may spend all your MD to summon the merest shred of your Legendary Power, manifesting either as an item, creature, or change to your very being.