Lyon Vastia serves as the ace mage of the Lamia Scale guild and a candidate for S-Class. His rivalry with Gray Fullbuster originates from their shared apprenticeship under the master ice mage, Ur. Initially introduced as the antagonistic "Sub-Zero Emperor Lyon" during the Galuna Island arc, he orchestrated the Moon Drip ritual to thaw the demon Deliora—frozen by Ur's Iced Shell—intending to defeat it and surpass his teacher. This ambition stemmed from a decade-long grudge, fueled by his belief that Gray indirectly caused Ur's death. Defeated by Gray and confronted with the truth of Ur's sacrifice, Lyon abandoned his destructive path and joined Lamia Scale, though his competitive dynamic with Gray endured.

He possesses a slim, muscular build, bluish-silver hair styled in upward spikes partially covering the left side of his face, and eyes with dark pupils accentuated by surrounding dark lines. A distinctive left-ear snowflake-shaped earring varies in size across appearances. His attire evolved from the imposing Sub-Zero Emperor outfit (featuring a skull-like helmet, white cape, and armored greaves) to Lamia Scale's guild garments: typically a dark high-collared tunic with decorative motifs, a fur-trimmed white jacket, snakeskin-patterned pants, and later a mantle with jagged edges. The Lamia Scale guild stamp is on his right pectoral.

Lyon's personality blends cold composure with intense ambition and impulsiveness. He takes pride in his magical prowess, initially driven to exceed Ur's legacy regardless of cost, leading to reckless actions like reviving Deliora or charging into battles without strategy during the pursuit of Oración Seis. Despite arrogance, he demonstrates sharp observational skills, deducing opponents' weaknesses mid-combat, such as identifying Racer's time-manipulation magic by observing birds. His emotions frequently surface in his rivalry with Gray, whom he constantly challenges to prove superiority, though underlying mutual respect exists, shown by Lyon's distress when Gray appeared fatally injured. Lyon harbored persistent, unrequited romantic feelings for Juvia Lockser, openly pursuing her despite her discomfort, before shifting his affections toward Meredy after the Grand Magic Games.

As an Ice-Make Mage, Lyon specializes in "Dynamic Ice-Make," crafting animated ice constructs like eagles, tigers, dragons, and panthers that attack autonomously. He also uses "Static Ice-Make" for non-living objects, creating swords, shields, cages, and clones. His notable spells include:
- **Ice-Make: Diamond Cage**: A near-unmeltable spherical prison weakening with distance from the caster.
- **Ice-Make: Water Serpent**: A serpentine construct freezing targets on contact.
- **Ice-Make: Clone**: A lifelike ice duplicate for evasion.
He employs basic Ice Magic for freezing objects or enemies and Snow Magic for generating blizzards. His combat style integrates hand-to-hand proficiency, exploiting opponents' injuries, and tactical ingenuity. A limitation is unstable one-handed ice molding, contrasting Gray's two-handed precision. Lyon holds immunity to cold-based attacks and partial resilience to snow magic.

Key relationships include:
- **Ur**: His revered mentor; her sacrifice to seal Deliora became his obsession, driving his early actions.
- **Gray Fullbuster**: A rivalry beginning in training, intensifying after Ur's death, evolving from hostility into grudging camaraderie, with Lyon later aiding Gray against threats.
- **Juvia Lockser**: His infatuation caused friction with Gray, including a bet during the Grand Magic Games; after repeated rejections, he accepted her lack of reciprocation.
- **Meredy**: Post-Grand Magic Games, Lyon developed mutual attraction with her.
- **Lamia Scale**: As the guild's ace, he collaborates with members like Sherria Blendy and Jura Neekis, occasionally displaying arrogance regarding their capabilities.

Lyon's story spans key arcs:
- **Galuna Island**: As Sub-Zero Emperor, he sought to resurrect Deliora; defeated by Gray, he acknowledged Ur's choice and joined Lamia Scale.
- **Oración Seis**: Allied with Fairy Tail in the Allied Forces, showcasing tactical acumen against Racer.
- **Grand Magic Games**: Competed for Lamia Scale, confronting Gray and Juvia's dynamic while beginning his interest in Meredy.
- **Alvarez Empire War**: Participated, demonstrating loyalty to his guild and allies.
Post-series, he maintains his role in Lamia Scale, with his rivalry with Gray continuing amicably and his romantic focus shifted to Meredy.