Rarest koi?

[elephantnose333464 19]

What is the rarest breed of koi(i.e. kin kikokuryu, kuro goshiki, ki utsuri) you have kept and why? And have you kept any of those breeds in these pictures?

 

[emeraldking53 104]

I've kept all four in those pics. Btw, there are different kinds of goromo koi.
When stating which kind happened to be rare which I've kept, I'd stick to the Ki shusui.
I'm also a huge fan of a good looking midori which seems a bit translucent because of a certain shine it's got.