All these talking made me remember a Hungarian comic book - would have been three volumes, only two were published - about ninjas. Quite a few aspects of Japanese culture were conveyed by them there was a scene with sumos as well. Too bad I barely remember, I have somewhere those comic books, couldn't find them yet.
I looked up the author since his doctorate is noted by his name. He is an economist surprisingly, but he was an organizer of six karate world championship, so I assume he has a passion for martial arts, and Japan.