When Soma and his companions cross paths with Aina on her way to visit her father-the Dark Lord-they decide to accompany her to the castle that lies deep in the forbidding mountains of the land of the devils. There, Soma discovers that the mystery-shrouded Dark Lord and the renowned hero Sir Iori are the same person: Iori Kanzaki, Soma's old friend from a past life. The reincarnated friends begin to put the pieces together: how the devils came to be, what happened between their nations, and why the two have been brought together once more. But as they do, a plot is brewing among the former Dark Lord's faction, soon to reach a boiling point.