Shinka no Mi: Shiranai Uchi ni Kachigumi Jinsei Temporada 1 Episódio 4

Seiichi and Saria train under Artoria to become adventurers. During their training the three of them are teleported into a dungeon by a demons trap. The dungeon they find themselves in the stronghold of the Black Dragon God, the strongest member of the Demon Lords Army. Artoria gets separated from Seiichi and Saria in the dungeon and the giant Black Dragon God appears before her. Then that overwhelming threat attacks! Can Seiichi and Saria save her in time?!