Stiyl Magnus is a magician of the Anglican Church's Necessarius division, specializing in rune-based fire magic under the magic name Fortis931, meaning "I prove why my name is the strongest here." He is a tall young man with shoulder-length blond hair dyed red and styled on either side. His attire consists of a black priest robe, and he wears a silver ring on each finger, earrings in both ears, and bears a barcode tattoo under his right eye. A heavy smoker, he is seldom seen without a cigarette and openly claims a world without nicotine would be hell. He dislikes Academy City due to the difficulty minors face obtaining cigarettes there. Though only 14 years old, his height and demeanor frequently lead others to mistake him for an adult. Roughly two years before the main events, Stiyl partnered with Index Librorum Prohibitorum and Kanzaki Kaori, traveling worldwide to copy the original grimoires stored in Index's mind. They grew close, but church authorities informed them that Index's brain had reached its capacity from holding 103,000 grimoires. Her photographic memory prevented her from forgetting unnecessary information, a condition that would eventually kill her. The only solution was an annual memory erasure. Stiyl and Kanzaki witnessed Index's physical decline and performed the erasure themselves, a traumatic act they carried out in tears. Afterwards, they attempted to rebuild their friendship with Index, but the prospect of repeating the memory erasure annually became too painful. They withdrew, leading Index to misinterpret their intentions and view them as enemies seeking the grimoires in her mind. Stiyl and Kanzaki allowed this misunderstanding to persist, believing it would spare Index the grief of forgetting her friends. It was following this memory erasure that Stiyl acquired his barcode tattoo, ear piercings, and rings. He made a promise to always protect Index, though the precise timing remains unclear. When Index later fled to Academy City, Stiyl and Kanzaki were dispatched to retrieve her. Stiyl became the first magician antagonist faced by Kamijou Touma. He attacked Touma with fire magic upon discovering him with an injured Index. Their initial battle featured Stiyl's rune spells written in ink on paper, which Touma neutralized by activating fire sprinklers. Stiyl subsequently upgraded to laminated, waterproof rune cards. He summoned a powerful fire entity named Innocentius, posing a serious challenge, though Touma ultimately defeated it and rendered Stiyl unconscious. Afterwards, Stiyl and Kanzaki observed Index living happily with Touma. Stiyl confided in Kanzaki his dismay over their role in repeatedly taking away Index's happiness, revealing his deep care and regret. Short-tempered yet fundamentally kind, Stiyl cares deeply for Index and has hinted at affections toward her. He does not particularly like Kamijou Touma and often enjoys causing him discomfort, but respects Touma's abilities and acknowledges that Index can be happy with him. Stiyl also handles the antics of his superior, Laura Stuart, and does not hesitate to punish her when she oversteps. Physically, he is quite weak—a side effect of the immense energy demanded by his magic, especially for maintaining Innocentius, which leaves his body frailer than average. As a skilled rune magician, Stiyl has fully analyzed the standard twenty-four character runes and developed new powers using a set of six. His primary tools are pre-made rune cards enabling rapid spell activation without on-site carving. Initially using paper cards with ink, he switched to laminated, waterproof versions after his defeat by Touma. These cards often display magic circles with inverted pentagrams and rune marks. Stiyl specializes in fire magic, manipulating flames burning near 3000 degrees Celsius. He commonly conjures Flame Swords and can wield two simultaneously for a technique called Squeamish Bloody Rood, scissoring enemies horizontally from both sides. He also generates explosions and varied fire forms. Beyond offense, he uses fire and heat for sensory and illusionary purposes—detecting hidden individuals via body heat and crafting intricate heat-based mirages with up to three dummy layers to mislead opponents tracking his magic. His expertise includes healing burns and even altering physical appearances by burning and healing facial wounds to reshape features, as performed on Aureolus Izzard. He also employs cigarette smoke to create symbolic patterns for transmitting messages through the air. Once, alongside Theodosia Electra, he executed a diagnostic spell using cigarette smoke and matches to analyze a mental attack on Patricia Birdway, replicating the condition within his own brain to devise a countermeasure. In the "Miracle of Endymion" movie, Stiyl appears among a trio of elemental witches attacking Kamijou Touma and Index. He utilizes an unboosted, one-shot version of Innocentius to destroy one of the Endymion's explosive bolts, displaying considerable destructive power. A side story details Stiyl's mission in Academy City involving Patricia Birdway and Theodosia Electra. He disobeys questionable orders from Necessarius to capture Patricia, who possesses no magic knowledge but is targeted for her ties to the Dawn-Colored Sunlight magic cabal. During the mission, he protects Patricia and Theodosia from other magicians, including one armed with a potent fire sword called Lævateinn. Stiyl employs strategic skill and illusion magic to evade attackers and works to secure an item named "Donati's Horoscope" to prevent broader conflict. In a collaboration event with ALICE, Stiyl arrives in the ALICE environment through unknown means, initially grouped with Misaka Mikoto, Shirai Kuroko, Kanzaki Kaori, and Tsuchimikado Motoharu and Maika. Upon seeing Kamijou Touma with Index and Sei Shōnagon, he initially blames Touma for their situation and attacks with fire magic before being calmed down.