Boon of the Weave (5e Epic Boon)
From D&D Wiki
Boon of the Weave
Prerequisite: The ability to cast at least one 9th-level spell.
Choose a 9th-level spell from any class spell list. You add that spell to one class spell list of your choice that you can cast 9th-level spells with (Though only for you), and learn the spell. You always have this spell prepared, and it doesn't count against the number of spells you know or can prepare. You can gain this boon multiple times, choosing a different spell to learn each time.