+atk/-spd Eldigan

as for the build, just go with a standard one (that isn't double fury) and yes you should upgrade his weapon for fury, its such a great upgrade and it makes every other refine basically worthless (unless you want 1 more point of Def or Res at the cost of 3 more attack)

I think since weapon refinery Eldigan runs a Brash Assault/Desperation build quite well. This build doesn't care about speed whenever you are in BA/Desp range, because you double no matter the speed.

And yes. That double Fury is too good to pass up. It makes him hit harder and be tankier at the same time, and helps him fall more safely into BA/Desperation range.

You could also run a Distant Counter build with Quick Riposte seal and Vantage B skill or QR B skill/Distant Defense seal, but that's more expensive and I'm sure he will still do a ton of work without it.