>>98592405If you rolled Zenobia, move her to
Zeke when he joins your party, if you rolled Finch, move her to
Morag when she joins. Other Rares you might have rolled on Rex aren't that vital to move over, because you can find enough guaranteed drop cores containing specific (and useful) Rare Blades through story progression and sidequest to fill your party up. If you haven't opened the Beastly Core you get in chapter 3 yet, don't, wait for
Zeke. In fact, every core you get through sidequests (Vess, Praxis, Kassandra, etc.) you should assign to the proper party member (Healer, Attacker, Tank) that isn't Rex.
The thing is, starting from chapter 8,
Rex gains the ability to equip all Blades, even those assigned to other Drivers. I wish the game at least hinted at that before I opened a bunch of Rares on him. 
