The .nsp format indicates this is the raw installation file used for the Nintendo Switch system.
Here is a solid write-up based on available information about this title: Overview: Mermaid Story (NS/US) Puzzle / Casual System/Region: Nintendo Switch (US) Publisher/Developer: DMG Ice Theme: Underwater/Mermaid aesthetic Mermaid Story [01000FC01977E000][v0][US].nsp.rar
Based on the identifier provided, (specifically with the 01000FC01977E000 title ID and v0 US NSP format) is a relatively obscure puzzle-themed game developed for the Nintendo Switch. aimed at a casual audience
Designed to be accessible, likely targeting casual players or younger gamers. Where to Find This title is primarily found on the Nintendo Switch eShop . and often "cute" or kawaii artwork.
Child-friendly or, at minimum, aimed at a casual audience, utilizing bright,, colorful, and often "cute" or kawaii artwork.