Yuuno Scrya, a member of Midchilda's archaeological Scrya clan, was orphaned young and raised communally. At age nine, he unearthed the potent Lost Logia known as Jewel Seeds during a dig. After alerting the Time-Space Administration Bureau (TSAB), their retrieval ship suffered an attack over Earth, scattering the artifacts. Yuuno journeyed alone to Earth for recovery, his clan's absence unexplained. An early clash with a Jewel Seed monster inflicted severe injuries, prompting him to assume ferret form—an innate shapeshifting ability practical for archaeology and conserving energy during healing—to evade human notice. Discovered injured in this form by local girl Nanoha Takamachi, who possessed latent magical potential, Yuuno contacted her telepathically. Entrusting her with his bombardment-focused Intelligent Device, Raising Heart, despite his own incompatibility, he guided her in using magic to locate and seal the Jewel Seeds, serving as her primary instructor in foundational spells and combat. Nanoha initially remained unaware of his human identity, leading to comedic misunderstandings like her changing clothes near him or taking him to hot springs. He later revealed his human form, establishing their partnership as equals. Specializing as a Force Field Mage under the Midchildan system, his magic emits a green hue. His Barrier Jacket features a green-and-cream tunic over shorts and a tan cape. Holding an A-rank synthetic magic rating, he possesses minimal offensive power but excels in defensive and support magic: barrier generation, binding spells like Chain Bind, mass teleportation, healing (Physical Heal), and search magic. He adeptly multitasked, maintaining combat while preparing complex spells or analyzing multiple data streams. His aerial combat skill and field manipulation allowed him to conceal battles or trap opponents. Post-Jewel Seed incident, dimensional disruptions stranded Yuuno on Earth for six months. He later aided Fate Testarossa's TSAB legal defense before becoming a librarian at the Infinity Library. During the *A's* conflict, he researched the Book of Darkness and fought the Wolkenritter alongside Nanoha and Fate, his scholarly insights proving vital to understanding the Book and creating the Unison Device Reinforce Zwei. Six years later, in the *A's* epilogue, he rose to Chief Librarian, adopting glasses and a ponytail tied with one of Nanoha's ribbons. By *StrikerS*, he appeared sporadically as a relic expert, advising during auctions and researching artifacts like the Saint's Cradle, no longer engaging in frontline combat. He maintained close friendships, supporting Nanoha and Fate's adoptive daughter Vivio in *ViVid* through library visits. Yuuno maintained unrequited romantic feelings for Nanoha, hinted by his enduring attachment (e.g., keeping her ribbon) and confirmed in supplemental materials. Their relationship stayed platonic, with Nanoha forming a family with Fate. Spin-offs like *Gears of Destiny* occasionally referenced this humorously, mocking his ferret form or romantic situation. Alternate continuities, such as the *Reflection* and *Detonation* films or the *INNOCENT* manga, diminished his role, depicting him solely as Nanoha's pet ferret or omitting him from key battles.