I was going to say something similar to what @jasonlint brought up. It’s a bit like how りるろられ are used for bith l & r sounds, because–similar to Spanish “r”–in Japanese the “r” sound is actually an alveolar tap (which is why you get the trilled “r” in both Spanish and [to a lesser extent] in Japanese). So this sound English-speakers hear as “r” is percieved as the same or pretty close to our own r/l sounds by native Japanese speakers.
The same with “V”–in Spanish (and Japanese) “b” and “v” are represented by the same sound. just that, while Spanish differentiates between “v” and “b” in spelling but not in speech, Japanese spelling and speech only represent this sound with びばぼばべぶ.
Actually, after thinking through all of that, I think it makes about as much sense to use ヴ in Japanese as it does to use V in Spanish. Like, it’s there, but it’ll still be pronounced as “b,” right? (That “right?” isn’t rhetorical btw–I’m no expert, obviously.)
…Does this make sense, or is it just a rambly word-pile?