I propose that once a weapon reaches max level at 5 star (were just going to imagine there a radiants o'plenty) it can be upgraded to a ultimate form, much like the battle sprites and to be ready for a potential tier 4. so strap in this is going to be a long one.
some things carried over from battle sprites are:
-2 options for the upgrade
-they will need a ultimate upgrade crystal of some sort, for, say at the cost of 1000 energy.
---the 2 upgrade options will be "combo master" or "overcharge" lets use (CM) and (OC) as abbreviations