Been fooling around with some ToD2 stuff lately (and far from done doing so)
Could it be that Rave should be Lave?
lave
1 /leɪv/ Show Spelled Pronunciation [leyv] Show IPA verb, laved, lav⋅ing.
–verb (used with object)
1. to wash; bathe.
2. (of a river, sea, etc.) to flow along, against, or past; wash.
3. Obsolete. to ladle; pour or dip with a ladle.
–verb (used without object)
4. Archaic. to bathe.
(farfetched, yes, but I wouldn't exclude anything)
So you basically take a dip in stings, wash yourself with some good ol' pain.
(Or maybe it just is "rave", as in the meaning of a "swarm/many")
No idea what this thing looks like in both ToD2 and RM2, but mixing physical skills and spells like that wouldn't sound like a big impossible no-no in my book... +in the case of the RM2 pirate's skill... I wouldn't be amazed if they probably just thought it was funny that it almost sounds like stingray :/