Fennekin served as the primary antagonist during the first arc of Greetings Adventurers. Initially posing as an ally, Fennekin, as the Cleric of Erathis in Caer, swore that he could remove the explosive devices from the heads of Aludra Wyrmsbane, Thom Vidalis, Tum Thumble, and Junpei Iori, if they bring him three powerful artifacts: The Whip of Binding, The Orb of Endless Power, and The Brazier of Worlds. During their journey (after Tum died and Junpei left), Fennekin kidnapped the family of Lord Titus Harper and used them as leverage to manipulate him into joining the others, and bring him, in secret, the Brazier of Worlds. He also kidnapped the sister of Ros, for secret later purposes. Harper did join the others, but was caught trying to steal the Brazier, and revealed to the others of Fennekin's treachery. Undeterred, they brought him the three artifacts anyway, and, with little to no plan, confronted him. In one of the most cinematic and dramatic episodes of the series to date, Fennekin revealed his plan: to combine the three artifacts, and use them to open a portal to the Abyss, bringing forth a horde of demons to ravage the land. The reason for this treachery? Fennekin was never a Cleric of Erathis, but one of Orcus! He detonated the devices in Thom and Aludra's heads, killing them. Harper was stabbed in the heart by Ros, and Fennekin, hardly the man of honor, killed (most of) Harper's family anyway, and Ros' sister.
After the real Erathis brought back the three heroes, and an Adherent, Jaela, Fennekin's army decimated the world, killing billions. Eventually, there was a mighty battle between the then un-named Ätlän-tã Fælcons and Fennekin, where he adopted the visage of Orcus himself. Thom Vidalis sacrificed himself to kill Fennekin, by swinging the Hammer of Sundering at him while he was holding the Brazier that was making the portal. This move killed Fennekin, destroyed the Brazier, closed the portal, and ended the Demon Apocalypse.