Gavin, operating under the alias Haku, holds the position of police captain in Koibana City, a role masking his true assignment as an Evol agent focused on supernatural investigations. He is Shaw's older brother; their once-close childhood bond has since become strained. During high school, he was two years senior to the story's protagonist, who addresses him with the honorifics "Gavin-senpai" or "Haku-senpai." Childhood trauma fuels his adult anxiety about losing those close to him, driving his commitment to protective roles.

Physically, Gavin has a tall, athletic build. His chestnut brown hair is cut short with slight bangs, complementing light golden-brown eyes. A visible scar marks the area between his neck and left collarbone. He typically wears a light blue denim jacket over a white shirt with black pants.

Outwardly presenting as stoic, unapproachable, and sometimes arrogant, Gavin reveals greater depth through interactions with the protagonist. He possesses a strong sense of justice, consistently prioritizing others' safety above his own and showing empathy even towards adversaries. His personality combines loyalty, crisis-level rationality, and natural leadership, inspiring others to follow him. Beneath his reserved exterior, unexpected warmth emerges through small smiles and steadfast devotion to his trusted inner circle. His ISFJ personality type and Enneagram 6w5 reflect his need for security, intuitive reliance, and blend of loyalty with analytical caution.

Gavin wields the Evol ability of Wind Control, manipulating air currents for flight, environmental sensing, and tracking disturbances. He specifically uses this power to locate the protagonist by detecting her presence or emotional distress through wind patterns. No canonical drawbacks to his abilities exist. He is highly proficient in hand-to-hand combat and marksmanship, capable of intercepting bullets mid-trajectory.

His relationship with the protagonist evolves significantly. After she inadvertently saved his life by awakening his Evol through her piano playing during their school years, Gavin developed a protective commitment towards her. He frequently rescues her, using wind to locate her during emergencies; their dynamic shifts towards mutual reliance when she later saves him from experimentation. He prioritizes her autonomy, supporting her decisions without interference, and expresses dedication through actions rather than overt declarations.

Driven by his ideals, Gavin relentlessly challenges injustices, even confronting close associates when necessary. His character development involves overcoming initial emotional restraint, leading to deeper openness and unpredictable passion within intimate relationships. Professionally, he demonstrates strategic acumen during crises, coordinating evacuations or large-scale rescues, cementing his leadership reputation.

Personally, Gavin favors spicy foods and dislikes bitter flavors. Outside work, he engages in motorcycle maintenance and gardening, though he struggles with plant care.