[Snake]

Nevarious Riff's second use is not doing any significant damage for how much it costs to use in terms of Momentum (3M to prepare the buff, 4M to use it for damage, basically a whole turn) and FP (thanks to Action Repeat changes, 15 then 22 for a total of 37 FP), given it doesn't ignore protection nor Evasion, the damage is kind of tiny. But I also believe it shouldn't ignore any of those because it hits all foes regardless of distance.

My suggestion for it is simple. Can its damage part also scale from Sound ATK? So it ends in something like this:

Nevarious Riff

Plays a riff off the guitar, surrounding you with electrical bats for 5 rounds. While active, attackers will take Lightning magic damage equal to Electric Axe's UL if they hit you. You can reactive the skill to send the bats flying at all enemies, ending the effect but dealing Lightning magic damage equal to your Sound ATK + Lightning ATK + Electric Axe's SWA.

The weapon's potential's design alone is awesome, but I believe Sound ATK influencing its damage will be as thematic while serving to make it worth the whole 6M invested to use it. The damage it does currently is shy for its massive momentum cost, added to no longer benefitting from the lightning retaliation.