I used to dislike gunblade starting out but with fast enemies and bosses I find gunblade to be very good with fast damage. Not as strong as a sword though but still fun to use.

What's the best gunblade and how do I make it stronger?

in the moment the best gunblade you can get is Rivalate but that will change when the next weapon series start coming.

now to make then stronger is kind of limited because gunblades can only gain bonus from classes from non weapon skills, however that changes when Luster is released that has skills focused for Gunblades only. Outside of class bonus then affixing it, Gunblades use mostly MEL damage and a little of RNG.

Rivalate is very strong regardless of not having the stronger weapon series or not, especially affixed, welcome to the luster squad, little late but welcome nonetheless

Thank you! @Lwyu @Jamesmor

I haven't run into Plamnia or Diard items yet. Where do I get those?

EDIT: I just watched Keroppi video on Rivalte. Looks like Ultimate boosters are hard to get.