I've seen on some sites that mention you can release a Blade to gain materials that make creating new rare blades much easier. I can't seem to find any options for it yet. Is there a specific npc I have to talk to or is it unlocked via story, or something else?
Go to the menu screen, select ‘Blades’ and then ‘Manage Blades’. Press X to release a Blade. Doing so has the chance to net you a Booster. You can’t delete Blades that are assigned to a character.
(You also can’t delete blades that you’ve overdriven onto another character and I’d love to know how to fix that...)