Galeroth Felgrimm commands the Black Banner army from the Black Castle, relentlessly opposing the kingdom of Evermore. He dispatches assassins against King Fidelius Astrum and recruits mercenaries to fuel rebellion. Galeroth leads roughly 20,000 warriors, their might augmented by enchanted Black Banner armor; his magic ensures absolute control over any who wear it.

This Galeroth emerges as the hidden identity of Sedulus Astrum, Evermore's crown prince presumed dead. Given to Beladon during war, Sedulus built a happy family there. His life shattered when Evermore, commanded by his father, annihilated Beladon using the artifact Mornstar, killing his family. This ignited his crusade for vengeance against Evermore and his own kin, especially his younger brother, King Fidelius. Consumed by betrayal, he operates dual identities: Galeroth Felgrimm assaults externally, while Gnauss Wisden, Evermore's royal magic minister, manipulates from within.

Galeroth knows of "Wayfarers" like Haruto Ichihara, who travel between worlds. Exploiting this, he lies to Haruto about soulmates—individuals linked across worlds—claiming sacrificing one saves the other. His deception aims to trick Haruto into killing Princess Astrid (Fidelius's daughter and his niece), falsely promising it would save Kotona Takashina (Haruto's girlfriend and Astrid's counterpart). In truth, linked souls share fate; one's death dooms the other. Galeroth seeks to absorb Astrid's vast magic for ultimate power to crush Evermore.

His rebellion climaxes in a direct assault on Evermore. Merging his identities transforms him into a monstrous One-Winged Angel. Confronted, he meets his end when Haruto impales him through the head using Mornstar. His death concludes his vengeful campaign.