Really want to read that just because of how ticked off Wakasagihime is.

Cosmos-Unknown said:

Really want to read that just because of how ticked off Wakasagihime is.

I'm reading it as ベチ, aka bechi which according to google is the sound of something sticky or gummy.
However, it could also be a repeated, shortened form for ペチャ, aka pecha, which is a slapping sound.

From context, I think it's the latter - Kagerou slapping Waggysaggy in the face with the weapon (which would line up with the little visual impact effects).

So it's probably Kage slapping waggy in the face over and over, which is roughly how Canynes wield their weapons in MH.