The third part in an anime film trilogy adaptation of the Donten ni Warau Gaiden spinoff manga.
 
One day, Soramaru is attacked by a mysterious man with large snake scales. The mysterious man somewhat resembles Tenka and demands to know where Tenka is. Soramaru later finds that this man was the result of an experiment using cells of the Orochi. While Soramaru and members of the Yamainu search for answers, they will uncover many secrets, and fight old friends along the way in search of the truth. 
 
(Source: Eleven Arts)