Lyon Vastia, an orphan seeking strength, sought out the formidable ice mage Ur. Adopted and trained as her disciple, he mastered Ice-Make magic from a young age. Ur later adopted another orphan, Gray Fullbuster, sparking a rivalry between the students. Deep resentment took root in Lyon after Ur sacrificed herself to seal the demon Deliora using Iced Shell magic. Unconscious during the event due to Ur freezing him to stop his interference, Lyon was told by Gray that Ur died fighting Deliora, not the truth of her sacrifice, to prevent Lyon from freeing the demon. This fueled Lyon's decade-long grudge against Gray, whom he blamed for Ur's death.

Driven by a desire to surpass his mentor, Lyon gathered followers scarred by Deliora and relocated the frozen demon to Galuna Island. Adopting the alias "Reitei Lyon" (Sub-Zero Emperor Lyon), he initiated the Moon Drip ritual to melt Ur's ice and revive Deliora, intending to defeat it himself. He ordered his followers to destroy a village hindering his plans. When Fairy Tail members, including Gray, arrived on an unauthorized mission, Lyon confronted them. After initially defeating Gray, Lyon faced him in a decisive battle. Despite Lyon's mastery of advanced dynamic Ice-Make, creating living constructs like eagles, dragons, and apes, Gray triumphed. The revived Deliora crumbled instantly, its soul long destroyed by Ur's ice. This revelation forced Lyon to confront his futile quest and his mentor's irreversible loss.

Following this defeat, Lyon heeded Gray's advice and returned to the legal guild Lamia Scale with his followers, becoming a prominent member. His personality evolved from cold and arrogant to more cooperative, though a competitive streak toward Gray remained. During the Oración Seis arc, Lyon represented Lamia Scale in the alliance against the dark guild. His strategic intellect emerged when he deduced Racer's time-slowing magic by observing birds mid-battle. In a critical moment, he sacrificed himself by tackling Racer off a cliff to save Gray and his comrade Sherry Blendy. Surviving the encounter, he later aided the alliance by crafting large-scale ice structures, such as wings for the airship Christina.

Lyon's relationships evolved. He ignored Sherry Blendy's affections but developed an instant infatuation with Juvia Lockser upon meeting her, frequently attempting to win her over despite her disinterest. Years later, during the Alvarez Empire arc, his attention shifted toward Meredy of the Seven Kin of Purgatory. His dynamic with Gray remained a mix of rivalry and mutual respect, exemplified when Lyon tearfully called for healing after Gray's apparent death and collaborated seamlessly with him in battle.

Specializing in Ice-Make magic, Lyon generated and molded ice into complex forms. His "Dynamic Ice-Make" focused on animate creations like animals, contrasting Gray's static constructs, though Lyon could also produce static objects such as swords or shields. Key techniques included Ice-Make: Eagle for precision strikes, Ice-Make: Snow Dragon for heavy assaults, and Ice-Make: Wing for aerial mobility. He demonstrated high resilience to cold-based attacks and quick tactical adaptability. His green-blue guild mark was placed on his right pectoral.

Physically, Lyon possessed a slim, muscular build with spiky bluish-silver hair often veiling his left eye. Early outfits featured ornate armor and a skull-like helmet as "Reitei," later replaced by simpler attire with snake-skin patterned pants after joining Lamia Scale. Post-seven-year time skip, he wore a dark tunic with a mantle and a larger chain earring.