You can purchase and download the game directly from the Nintendo eShop. Since this is a Japanese release, you may need a Japanese Nintendo account and eShop credit to complete the purchase.
Buying the game directly supports Koei Tecmo and encourages them to continue remastering classic titles.
The download of as an "nsp" or "rar" file from unofficial sources is a violation of copyright law and risks exposing your device to malware. Instead, you can legally enjoy this classic strategy game through authorized digital and physical platforms. How to Legally Play Taiko Risshiden V DX