At the title screen, choose Options. In the Options menu, move down to the "S.E." command and use the B button to play these songs in order: "He Runs," "Japonesque," "Shinobi Walk," "Sakura," and "Getufu." Exit the Options screen and start your game. You are now invincible!
Here is a handy hint to boost your score. Go through the hold stage without using your shurikens. If you manage this feat then you will be rewarded with 30,000 points in your Shinobi Bonus. I have been told you get a 50,000 points for not using your sword but I haven't pulled that one off yet.
At the start of the game go to the the options menu. Change your limit of shurikans to 00. Then, wait or hit or hold the C button for a while, then it changes to unlimited mark. You should have more things !