Just finished off a second batch of the sourdough shokupan. Made double the amount and gave the additional loaf to a friend of LapGirl’s on her request.

It doesn’t have yudane, nor the long fermentation of the 3 step/day process Pain de Mie, but the sourdough does introduce some of that tang. For the effort and time taken and the result I get, am perfectly satisfied. No milk, no eggs, just a little butter, but extraordinarily rich tasting - heaven!
The recommendation is to use a natural yeast nurtured from raisins, but I just added my usual sourdough culture (fed with white flour). But I also added 2g of instant yeast so that it wouldn’t take too long to rise and develop too much of a sourdough flavour. The first proof took about 2 hours.
The resulting loaf isn’t as robust as the Yudane Pain de Mie - needs a little care when slicing so it doesn’t compress - but it’s so delicious, and way too easy to eat too much of (I don’t have a Pullman loaf pan, it’s fine without it)