I'm stunned speechless. I think I've just discovered
the most probable source material for Hasekura's novels. And if I'm right, he couldn't have chosen from a richer source.
The Golden Bough, by Sir James George Frazer, first published in two volumes in 1890. The Wikipedia entry for this book, which supposedly laid the foundation for modern anthropology, particularly in the study of "pagan" myths and magic, can be found
here.
The Golden Bough: A Study in Magic and Religion is a wide-ranging comparative study of mythology and religion, written by Scottish anthropologist Sir James George Frazer (1854–1941). It offered a modernist approach to discussing religion, treating it dispassionately as a cultural phenomenon rather than from a theological perspective.
So what's the big deal? Well, Sir Frazer was apparently the first anthropologist to notice this particular ritual that is supposedly shared by many farming communities around the world: the
Corn Dolly. Take a read for yourself to see the origins of Horo, the Corn-Wolf. It's amazing! (Even if the theory is probably widely discredited by now...)