If you are playing the digital PS2 Classic version available on the PlayStation Store (for PS3/PS4), some downloaded save files can cause conflicts with the game's "Data Install" feature, causing the game to freeze on the loading screen. Always check if the save file is flagged as "corrupt" by the system menu before booting the game.
Released on the PlayStation 2, this title is the pinnacle of the Ultimate Ninja series. Having a "100% Complete" save file allows you to skip the grind and dive straight into:
Complete save files (usually YouTube or gaming forums.