Since you're going with dual-wielding swords, you might as well go all the way with the FF5 references and name the Ultima Blade mode "Spellblade Barrage" and turn it into a machinist-esque heat mode with lower recast times to go with the OCD reset.

Being able to activate the mode before 100% is also essential. It's probably tempting to have a "super god mode" but that doesn't mesh well with party buffs and variable encounter designs that won't let you use it ASAP.