It looks like you’re referencing a ROM or game file naming convention for Pokémon: Let’s Go, Pikachu! on Nintendo Switch (NSP/XCI format, likely including an update file).
Indicates the file includes or is a specific software update. Below is an essay examining Pokémon: Let's Go, Pikachu! Pokemon- Let-s Go- Pikachu- Switch NSP XCI -Upd...
Do not search for “Pokemon Let’s Go Pikachu NSP download” online – those are pirated copies. Instead: It looks like you’re referencing a ROM or
or emulated game backups for the Nintendo Switch. Specifically: NSP (Nintendo Submission Package): Pikachu! on Nintendo Switch (NSP/XCI format