Mattalast Ballory is a First Grade Armed Librarian at the Bantorra Library, ranking among its five strongest members. Entrusted with the secret of Heaven, he shoulders the duty of protecting this knowledge. Promoted at fifteen as a child prodigy, he once performed with a friend at the illegal Drowned Dog pub. He carries a pipe inherited from his grandfather.

A well-built blonde man with yellow or blue eyes, Mattalast is often seen smoking his pipe. His sharp-dressed appearance features a black tuxedo, bowler hat, and bow tie. In youth, he wore long flowing hair—colleague Mirepoc Finedel deemed it hideous—before adopting a shorter style during his relationship with Hamyuts Meseta.

Personality-wise, Mattalast presents as easy-going but is consistently perceived as a liar. His history includes promiscuity with multiple women before romancing Hamyuts Meseta, whom he recruited to the Armed Librarians after meeting at the Drowned Dog. They cohabitated in his apartment, but the relationship ended. Unresolved feelings for Hamyuts resurface upon encountering her corpse, triggering a Heroic Blue Screen of Death. He grapples with inadequacy as she ascends ranks and surpasses his strength, embodying a "Can’t Catch Up" dynamic.

In combat, Mattalast wields firearms: a revolver and an anti-tank rifle delivering tank-cannon firepower. Though among the organization’s strongest, reliance on conventional arms renders him "Weak, but Skilled" compared to peers with large-scale destruction abilities. His supernatural Combat Clairvoyance foresees events two seconds ahead, enabling evasion and counters during rapid engagements. Activation manifests as supernatural gold eyes.

Key events include receiving orders from Acting Director Fotona Badgammon to kill Hamyuts—a task thwarted by lingering emotions. During the Shindeki Church conflict, he witnesses Hamyuts’ corpse and fights in Ruruta’s non-entity entrails, where fallen Armed Librarians are summoned. Post-dissolution of the Armed Librarians and public revelation of their secrets, Mattalast faces a unique death sentence. Avoiding execution, he dedicates himself to restoring books he destroyed to protect the library’s secrets. He seeks families and friends of deceased authors to learn their stories, inscribing narratives within his soul. His goal is to become a "collection" book upon death, preserving these tales eternally.