Here the Z-Sigil won't affect the set or weapon used.
The best weapon for this fight is either the Purge Frostsword "Shine" or the Nepa Icecutter "Shine" both share the same stats. Since the Premium Evo's only have mediem length a length up sigil will be very helpful.
Sigil 1: [ SnS Up 15 | Beam Slash | Length ]
Sigil 2: [ Element 15 | Element 15 | Element 15 ]
Sigil 3: [ Element 15 | Element 15 | Element 15 ] or [ Element 15 | Duration 12 | Wait Time 17 ]
This setup is pretty much set in stone.
You could try to use more crystals like Para or Power, but in my experience I haven't found a good opening where using them results in more damage.
After avoiding the initial explosion, roll the after explosion. Then position yourself on his right side and prepare an evade slash so you can get the i-frame on his bite.
Avoiding this move isn't the challenge. The trick here is to input an upslash after evading the second explosion so you can hit both hits of your beamslash on the arm. If you don't do the upslash you'll miss the first and more important hit of the beamslash losing out on damage.
Ideally you want to be positioned on the arm in a way that it will push you into the right position right on the outside of his arm. From there it becomes simple but in a run its very difficult to get this consistently. If you notice you're not in the right position extreme run to his arm and adv slash it to prepare an evade slash.