Astolfo Granatum hails from the Granatum lineage, bound by deep Catholic Church ties and a Chasseur legacy extending back to the War. Raised to uphold this tradition despite an inherent gentle nature that avoided conflict, he secretly befriended a wounded vampire child, sharing family secrets. This act triggered catastrophe: vampires invaded his home, torturing his family over days. Astolfo witnessed his mother violated before his father, who was then killed. He and his six-year-old sister endured repeated feedings, forcibly Marking him thirteen times; he held her hand as she died. Roland Fortis led the Chasseur rescue that saved Astolfo, leaving him the sole survivor. The trauma shattered him, inducing suicidal instability.

This forged an obsessive hatred for vampires. Charles, the Chasseurs' Commander and First Paladin, directed Astolfo to weaponize his tragedy, becoming a Paladin symbol for public support. Astolfo initially idolized his rescuer and trainer, Roland Fortis, as near-divine, but this morphed into profound resentment and contempt. Achieving Paladin status at fifteen—the youngest ever—he claimed the Garnet seat. His brutality escalated, exemplified when he slaughtered human survivors sympathetic to vampires during a raid, branding them heretics. Roland condemned his excess violence, prompting Astolfo to confess his self-loathing and desire for punishment over his family's deaths. Roland resigned as trainer to redirect Astolfo's hatred onto himself, cementing Astolfo's embittered, vengeful path.

Astolfo's androgynous appearance features fair skin, a round face with a small chin and nose, thin arched eyebrows, and large, upturned pink eyes with long lashes. His long, straight dark pink hair parts in the middle, cuts just below the chin, and covers his ears. He wears the standard Chasseur uniform: black pants, a cassock, a white harness, a purple ribbon-like belt, and white lace-up boots. Accessories include a red garnet rosary, fingerless gloves, and earrings resembling vampire fangs.

His personality radiates profound malice toward vampires and their sympathizers, openly declaring a Chasseur's duty is vampire extermination, not human protection. He shows scant regard for human life and relishes inflicting suffering. Quick-tempered, he rages over minor provocations—especially when mistaken for a woman, touched without consent, or compared to Roland. Violent, obsessive, egocentric, and sadistic, he pursues vampire genocide as self-proclaimed "justice." Fragmented traces of his former gentleness linger in kindness toward small children. His relentless pursuits verge on self-destruction, manifesting in reckless overdoses on combat-enhancing steroids.

His primary weapon is Louisette, the "Pillar of Justice"—a mechanized spear powered by Astermite that unpredictably extends mid-combat and generates explosive bursts after charging. He uses the Chasseur "tonic," injectable steroids boosting combat prowess at severe health risk, including bleeding from eyes and nose if overused. Standard gear includes Aegis grenades, specialized flashbangs blinding vampires and disrupting their World Formula manipulation. Lacking brute strength, he compensates with exceptional agility, speed, and tactical cleverness, employing rapid successive strikes and baiting opponents into vulnerability.

Key relationships drive him. His hatred stems from the vampires who murdered his family, particularly the unnamed young vampire whose betrayal prompted the attack. Roland Fortis, his savior, shifted from worship to hatred after an unspecified betrayal; Astolfo remains acutely aware of Roland's behavior. Marco serves as a loyal subordinate enduring physical abuse with unwavering devotion. Interactions with Noé Archiviste and Vanitas highlight his aggression; Vanitas deliberately provokes him by insulting his family and comparing him to Roland, igniting traumatic memories and fury.

The Beast of Gévaudan arc showcases his volatility and trauma. He murders human Dragoons mistaking him for a woman, excusing it as self-defense. Confrontations with Noé and Vanitas escalate as he injects tonic. Vanitas's taunts about his family trigger a breakdown. Encounters with Naenia's automatons force him to confront the five remaining Marks of Possession on his body, driving anguished screams and indiscriminate slaughter. In the castle battle climax, he overdoses on multiple steroids, accelerating physical deterioration. Fighting Noé, he recounts his family's torture before being overwhelmed by the drug and Noé's counterattack. A final mental collapse occurs when Marco calls him "young master," flooding him with memories of his sister's death and Roland's rescue. Sobbing and blaming himself, he stumbles toward Roland before collapsing unconscious. Roland carries him away.