Yuliy Jirov, known as Yuriychka, is a teenage Sirius werewolf whose life was shattered when vampires destroyed his village of Dogville near Moscow. This attack claimed his human mother Sachi and his Sirius father Alexei, who had previously departed to seal the Ark of Sirius. During the assault, his older brother Mikhail was turned into a vampire while protecting him, driving Yuliy to dedicate his existence to vengeance. This quest leads him to join the vampire-hunting Jaegers, operating covertly from Tokyo's V Shipping Company in the 1930s.

Tall with deep blue eyes and long, messy dark blue hair typically secured in a low ponytail, Yuliy bears a distinctive white streak near the left side. His veins and eyes emit a bright blue glow when his Sirius abilities activate. He favors practical combat attire: a pale blue fur-lined coat over a light blue shirt, dark blue jeans, black boots, a bright scarf, and an olive green jacket often tied around his waist. Intense rage or accessing deeper power levels causes the white streak in his hair to expand toward his bangs and ponytail.

Stoically reserved and unapproachable due to his solitary nature, Yuliy transforms into intense ferocity during battle. He exhibits protectiveness toward allies and unexpected gentleness with children, like comforting Saki Hanada after her father's death. His consuming drive for revenge fuels recklessness in vampire confrontations, frequently disregarding team safety – a single-mindedness rooted in survivor's guilt and trauma. He remains oblivious to romantic attention, such as that from Ryoko Naoe.

As a half-Sirius, Yuliy possesses enhanced strength capable of shattering a vampire's sword, agility to evade high-speed attacks, endurance for prolonged combat, and pain tolerance enabling rapid recovery from severe injuries like stab wounds. His heightened sense of smell detects vampires. Rage triggers his "beast blood," inducing a berserk state that amplifies his capabilities but renders him feral and indiscriminately violent, marked by sharpened fangs, glowing blue veins, and expanded white hair patterning. He wields a customized three-section staff with retractable blades, self-taught and lethal enough to kill royal vampires. Sealing the Ark of Sirius within his right eye grants him unspecified new powers related to the relic.

Yuliy's relationships center on loss and loyalty. He regards Jaeger leader Willard as a paternal figure, despite later uncovering Willard's indirect role in Dogville's destruction via archaeological research that exposed the village. Within the team, tensions simmer with Philip, who resents Sirius for his parents' death but distinguishes Yuliy from that blame. His most complex bond is with his brother Mikhail, now a vampire serving king Yevgraf; Mikhail repeatedly disobeys kill orders targeting Yuliy, hinting at lingering loyalty. Yuliy also forms a trusting partnership with Bishop, a former Jaeger turned vampire, recognizing his underlying integrity.

His character evolves from solitary vengeance toward accepting camaraderie. Initially isolating himself on missions to protect others, he gradually integrates with the Jaegers as a surrogate family. A pivotal confrontation with Willard over his past role in the village's tragedy sparks rage, yet Yuliy chooses not to kill him, signaling growth beyond retribution. His journey culminates in sealing the Ark of Sirius, with the act's full implications undisclosed.

Additional details include sensitivity to cold, self-taught combat skills, left-handedness, and a preference for biology as a subject.