Q: What weapons should I start upgrading? And where can I find the ultimate weapon for each character?
It depends on how you want to approach each individual character. Me, I tend to use Fang for Strength, Lightning for Equal approach and Vanille for Magic.
To get the ultimate weapons, you need to evolve the weapons to Tier 3. Tier 1 weapons (initial) level up to 25 before hitting *, Tier 2 level up to 60 before hitting *.
Yeah, Fang has overtaken Lightning in strength.
So, what's her best equal weapon?
Lightning's best equal weapon is Organyx, but you'll only be able to buy it once you unlock the Gilgamesh shop, further in post-game.
So far I found that her initial weapon, BlazeFire Gun works the best until you get Organyx
Don't se Organyx that's a bad idea the stats are good, but it has a -70% ATB charge effect meaning you're bars'll fill really slow its not really worth the extra attack.
Instead use the Lionheart series of weapons it only gives 508 STR and MAG at rank 3 max level but it has the quick stagger ability, which has a chance of staggerring the enemies even when the bars not full with every attack.