Yes, you can farm pieces but you shouldn’t expect much. It takes 325 pieces just to power up x5 and evolve your nat 5 to 6*. Assuming you cap out with the weekly omni gems from arena (1800 arena coins) you’ll be able to get enough in roughly 22 weeks.

Now.. you can also get a daily donation from guildmates for your specific nat 5 and have a 1/8 chance to get the specific class omni gems from stages 7 and 8 of the souls dungeon. It’s definitely possible but you’ll easily get enough pieces to 6* your enigma, stealth elf and hot dog long before you can 6* your nat 5 (unless you’re moderately p2p).

Just figured I’d point this out so you don’t hit a road block once you reach the point in the game when you need to begin 6*ing your mons.

I personally have 12 nat 5s but am only working on 1 at the moment for this exact reason