I don't know... I always sort of assumed that Sin was the water representative, being essentially created/rebuilt from the High Summoner's Final Aeon itself. I suppose that doesn't technically make it an Aeon, but...
Is there any particular reason it couldn't be both? ;) Just because something appears to absolutely bat-shit insane doesn't necessarily mean there's no logic behind it.
Of course, it's also entirely possible that Hojo may have just had a very odd fetish and had been spending a little too much...
I'm going with genetic engineering. The guy created a super soldier by splicing together DNA from Jenova with that of a human embryo, and attempted to breed a half-human/half-Cetra with Nanaki (who's species isn't even humanoid) to increase the offspring's lifespan.
WOOOOOO!!! :awesome:
... Never fails. Whenever it's my turn for something, there's inevitably some sort of delay. -_- I swear, the universe conspires against me, sometimes... :wacky: