Ok, ok, I know that Bade of the Immortal is a manga
(a GREAT Manga!) and is placed in Japan, but maybe Mr. Samura leaf through some books or he have seen on the web some pictures of these african knives (see pics attached). They come from Cameroon (Boumali and Gbaya tribes). You know contamination is one of the most important factor for fantasy
and the shape is very similar
