What happens to characters' weapons if they have demonstrated being summonable and aren't physically on the character's person, like Kingdom Hearts' Keyblades and the Nobodies' weapons? They seem to fit in something of a gray area.

And this is thinking kinda far in the future (sorry) but, if a person comes from a canon with powered/magical items, would those items work for people from different canons? For example, materia from Final Fantasy VII or Evokers from Persona 3?