Official Executioner for the Shogunate?

I've always read that the position of official executioner for the Bakufu was a fictional position, thought up by Kazuo Koike, for the manga, Lone Wolf and Cub.

However, I am reading a book titled, Behind the Face of Japan, which is another post in itself as it was originally written in 1934, and revised in 1942, that mentions the last of the official executioners, but not by name, so I couldn't research it through that means. 

However, coming across this tidbit of information has generated curiosity in my part to further research this subject more.