The initial knot is called a "single column tie", and there are a couple other videos on this site which cover it.

What I've done is, instead of forming a loop over the bight, I twist the bight over the working end, like in Gorgone's single column tutorial. It's slower than the loop method but makes more sense to my brain.

With reverse tension, you have to pull the entire length of rope through while tying and untying, which is rather slow. Forward tension single columns (including the Somerville bowline) are much quicker.

I see you're in Adelaide. Shibari Adelaide is run by an student of Kanna; if you go there then you'll likely learn a Kanna-style stemmed TK. I do recommend attending in-person classes, as I've found that many subtleties (e.g. how tight the wraps should be) are difficult to communicate over video.

Very clever! I wonder if the same technique can be used with the hands behind the back. Or with the thighs up against the belly.