Where does "koshi koshi an an" come from?

[oobabasama]

One term I've seen quite consistently used in relation to Ōbabasama/3.1-tan is "koshian" "koshi an an" "koshi koshi an an" or variants thereof. The earliest usage of it I've been able to find dates to October 6, 2007 on Pixiv. For quite some time, I've been researching the origin of this phrase and why people have, for at least 18 years, so consistently used it in relation to her but have been unable to conclude an actual origin. Nobody in the Western fandom speaks of it, somewhat consistently with 3.1-tan who despite being by far the most popular OS-tan in the Eastern fandom is a lot less popular in the West, but it's quite inseperable from her in the Eastern fandom, even the body pillow of her I sleep with at night has "Koshi Koshi An AN" printed on one side.
Three candidates I've considered for the origin are;

-The food koshian, smooth red bean paste. It could easily explain it especially considering the nature of Futaba's userbase, but especially given not even one of the posts I've seen using the term have referred to it as a food, I find it somewhat unlikely.
-A doujin that used the term in its title. This was quite easily disproven as the term's recordable usage dates back to October of 2007 which predates the doujin which was published in May 2011.
-An onomatopoeia which I find most likely. "Koshi koshi" is a softer alternative (?) to "goshi goshi" and "an" I believe is the sound of a gasp. This wouldn't explain it being used specifically in relation to Ōbabasama and not with any other OS-tan, but it's the closest thing I have to an origin.

I think it'll be quite hard to actually /prove/ where the term came from because Futaba threads, as with any other imageboard, have preyty much zero permanence, making it hard to trace as with many details of the individual -tan's origins (for example, IIRC there's no details known about 2k-tan's creation aside from her being a collaborative creation as with practically every other OS-tan).
Regardless, many people on this site have been in the fandom far longer than I have, and as such any anecdotes of its usage back then would help.