no, it's a expression for a naked tenko aka a divine creature naked.
If i recall correctly if you don't reach divine state like Tenshi or Ran, yur "nakedness" is only "Suppa", at least recalling that video dueling of Ran and Rinnosuke both go naked and Ran says "we are both suppa!"
Yeah, Tenko is primarily a term used for a kitsune that has reached the 'celestial' state. Although I've Seen Tenko used for Tenshi as well......
Anyways, Kitsune gain one tail for every 100 years they live, up to nine, that's a commonly known bit of information. What may not be so well known, is that after that point, the Kitsune will LOSE a tail every 100 years after that, until its down to only 4 tails, at which point it is considered a 'Tenko' and is only one step below the divine.
(What 'one step below the divine' really means is up for interpretation, as the information on kitsunes never really says what exactly that means.)
@JIE If Tenko really is just a way to refer to celestial creatures, I guess that would explain why the sometimes call Tenshi by that....
Well as you said, Tenshi is nicknamed Tenko so i think it may be a form of title or name for a Celestial, plus it has a funny sound maybe that's why it's used both for Tenshi and Ran memes even if Ran hadn't reached Tenko yet.