Regarding rare blades: do you have to use those strengthening items or are those just for raising chances? I mean those justice/courage/etc items that you *can* choose before using a core crystal.
Also: Are blades forever tied to the character who summmons them? Or will there be a way to switch them to another driver?
I think in my Japanese version its called the ideogram, or something, not sure if that's what the localized version calls it. But anyway, each character has a level for courage/justice/etc, and they raise as you unlock skills on their blades, or you can increase them temporarily using those items when you use a core crystal.
The items themselves correspond to elements (courage being fire and water, justice is light and dark), and I believe they have a direct effect on the % chance of getting a rare blade, and the element they end up being. The higher your ideogram levels, the higher your chance of getting rare blades.
I need to look up on some Japanese wikis to see if there's any ideas on what the chances are, but I've gotten rare blades from common cores with no items, and I've gotten common blades from rare cores with 5 items used, so at the end of the day it's all down to rng.
For giving blades to other characters, there are items called "overdrive", found in chests (and possibly available to buy at some point). You can use them by selecting a blade in the blade option on the main menu, and they'll let you move a blade to another character. I haven't used one yet, so I don't know if it completely swaps the driver, or if it lets multiple drivers use the same blade.