[Slydria]

My only concern is I think Fenrirs (in SL2 at least) are pretty distinctly ice themed based on everything we've seen about them. (Fenrirbus is Ice based. Fenrir spell from LB is Ice based. This weapon is Ice based.) So it's a little weird to suddenly add Fire and Lightning, even considering the reference.

I'm not against the idea entirely but this might be something to consider for a new weapon, say an alchemy recipe for a Chimera Nunchuck that uses Fenri as one of the component and in a way serves as a "+" version.

As for Fenri itself? I think it's mostly fine aside from it's unique Skill which could use a tune up since I believe it still operates on pre-GR numbers. (Bumping it's total damage to 100% SWA + 100% Ice ATK and making it function like Thousand Stab does now (where things like Armor applies once) would be nice, maybe with a chance to inflict low-level Freeze on the skill itself since it is called Freezing Round.)