How does the weapon leveling works?

[DmonHiro]

I know about upgrading weapons with the curator, but sometimes after a battle, I'm told that a weapon I have just leveled up. Sometimes it's not even the weapon that's equipped. How the heck does that happen?

[Null]

Originally posted by DmonHiro:

I know about upgrading weapons with the curator, but sometimes after a battle, I'm told that a weapon I have just leveled up. Sometimes it's not even the weapon that's equipped. How the heck does that happen?

Basically just think of it as weapons being dropped, and you're finding the same weapon you already had but at a higher level.

[Willow Rivers]

The enemy dropped a random weapon and you already owned it so it leveled up that weapon.

[Ratsplat]

Not entirely sure but it seems like defeating groups of enemies for the first time almost always gives you an upgrade. I think fighting the same ones constantly give much less or nothing at all item wise.