[TOMT] [JAPANESE MOVIE] [1980s]

I saw this Japanese film on instagram reels a few months back. It was the opening scene and heres how it went:

•Set in what looked like feudal Japan •A boy had dishonored his family •His mom handed him a tanto and told him, "Take this and kill yourself. You must leave home and never come back." •The boy walks off into the distance •As the boy is walking away, the landscape beyond him has clouds and a single rainbow over the entire sky

I think the movie name has the word "fox" in it. Not sure how much that helps.