Where to Watch Donten: Laughing Under the Clouds - Gaiden: Chapter 2 - The Tragedy of Fuuma Ninja Tribe (2018)

Fuma ninja clan is a secret ninja tribe that is waiting for the "Orochi" (gigantic snake) to resurrect for generations. Shirasu and his twin brother Ichiu grew up in this viscous environment and this tells how they become the leaders of the clan.