When you see discussions online about "NSP files," they generally refer to the digital version of a game. Unlike the physical cartridge (which uses a different format), an NSP file installs directly to the Switch’s internal memory or SD card. For Naruto Ultimate Ninja Storm , acquiring the NSP version legally means purchasing the game digitally through the official Nintendo store.
You are permitted to dump your own purchased copy of the trilogy into an NSP file using a hacked Switch (via tools like NXDumpTool ) for personal backup or emulation on PC (Ryujinx / Yuzu). However: naruto ultimate ninja storm switch nsp