Sister kata to Seiunchin?

I was just wondering if anyone knows the answer to this question? I've looked on the web, but can't seem to find an answer. Do any of you know?

As far as I know, seiyunchin kata exist in Goju Isshin Shito and Ruyei Ryu.
Version from Goju come from Miyagi - Higashiaonna - Naha-te or Ru Ru Ko(China).
Version from Isshin and Shito come from Miyagi.
The Ruyei Ryu version also comes from Ru Ru Ko to Norisato. So they could be sister versions.
Maybe Chito Ryu also has seiyunchin kata, if so it would be a Miyagi version.
Don't know if Kyokushinkai still practise seiyunchin, if so it comes from Yamaguchi - Miyagi.

Apparently SOCHIN is the "sister" kata.

Chris Caile posted some bunkai from both, they were different ways of dealing with the same threats.