well, it just a mutt of course, likely a cull from a doitsu kawarimono spawning- something Aoki is particularly good at.
This is a very interesting quiz however, because it proves that only the breeder knows for sure! It IS in a benching definition, a kujaku. Not exactly though as the sumi scale is suspect. There are tell tail signs of kawari in this fish- benikoki, kikokuryu or goshiki in the mix. But the koi must be doitsu to fill 'the punch line' that we are being set up for!
If no one accepts this explanation and insists the breeder calls it a metallic scaled or wagoi version of a oo-oo-ggagagoi of kumonryu origins- I have a scaled shusui I'd like to sell them!