I wonder if this was based of a picture of Erich Hartmann in a similar pose?
Seems like it, but nothing is mentioned in the Pixiv collection. I miss the days when each image had their own description.
EDIT: Seems the image has been deleted and I can't find a different copy. There being a photographer with the same name doesn't help. Suffice to say it looks a lot like the above image, but real Hartmann.