Demonia, also referred to as Demonium, is a Digital Friend in Shadowverse Flame and serves as the partner to the character Ryoga Jasei. Initially, Ryoga neglects Demonia, considering the Digital Friend to be weak and annoying. After Demonia runs off on his own, he is found and returned to Ryoga by another character, Itsuki Mitsutagawa. Following this incident, Ryoga keeps Demonia in his deck, finding him somewhat useful, though he continues to be cruel to the Digital Friend when battles do not go as planned.

Demonia has a very emotional and skittish personality. Despite the poor treatment he receives from his partner, he cares deeply for Ryoga and consistently demonstrates a desire for his approval and success. This loyalty becomes a key part of his motivation, as his primary goal is to be valued and to support Ryoga in his battles.

In the story, Demonia plays a crucial role in Ryoga’s character development. The turning point occurs during Ryoga’s second battle against Wolfram Zerga. When Ryoga is badly beaten and on the verge of giving up, Demonia refuses to let him be defeated, cheering for him loudly. This display of unwavering support causes Ryoga to finally recognize Demonia’s true value and understand his own reason for fighting. The strengthened bond between them allows Demonia to undergo a temporary transformation into a more powerful form known as Demonium, Crush Devil. This event marks a significant shift in their relationship, progressing from neglect to a genuine partnership. Demonia’s notable abilities are tied to this bond, with his primary power being the capacity to evolve into a stronger form when his connection with Ryoga is fully realized.