They're baaaaaaack! Rocky, Colt and Tum Tum in their first adventure since their last! Now, older, and more advanced. Grandpa now tells them they're ready to learn from a teacher in Japan. But before they can go, the boys have a baseball match which really takes a turn for the worse. Also, a childhood rival of Grandpa Mori Shintaro's (Funny, wasn't his last name Tanaka in the last movie? Oh well) by the name of Koga wants revenge for a past accident, and because Grandpa has in his possession a dagger from a championship match that he felt he should've won, so he sends his dimwitted nephew and two of his numb skulled buddies to Grandpa's house to get it. Rocky, Colt and Tum Tum meet them and really kick things up. Later on, Grandpa goes to Japan and get's in a cab accident, so the boys use "Ninjanuity" to get there and help. While in Japan, the boys make new friends and new enemies.