THE YOUTH AND HIS AMULET (1961)
Don't know much about this film except the blurb that seems to be on every website that mentions it:
"Gen is a lonely orphan boy. His sole sense of companionship comes from an imaginary friend, the god Prince Fudo-Myo. Prince Fudo-Myo comes to the boy’s rescue in times of difficulty."
Yes, that IS Toshirō Mifune as the imaginary friend Prince Fudo-Myo. Apparently Fudo-Myo (the Immovable Bright King) is a Buddhist guardian deity.
The director of the film is Hiroshi Inagaki, with whom Mifune-san made more films than with director Akira Kurosawa. Inagaki-san made many samurai films, including the classic The Samurai Trilogy, starring Mifune-san as Musashi Miyamoto. This time around I guess he decided to try his hand at a kids' film.
If anyone has seen this film or, better yet, knows where I can see it, please let me know. I would love to watch it for myself.