During a championship baseball match, the three brothers hear that their grandfather in Japan is in trouble, and head out to help him, conceding the match. When they arrive in Japan, they must use all their powers to defend him against his ancient enemy, who has returned to exact revenge — imdb.com
This is the movie that planted the seeds of fascination with Japanese culture, for that I am eternally grateful. Also, I probably watched this more than other film a a child. No, I have never seen the original 3 Ninjas or any of other ones that followed this one nor do I ever care to.