Yukine (雪音, Yukine?) (lit. sound of snow) or Haruki Tajima, his human name, is one of the three main protagonists and one of Yato's Shinki. When the name Sekki is called, he transforms into a silver Ōdachi, the handle of which is loosely wrapped in bandages. After becoming a Hafuri Vessel (Blessed Regalia), his new Shinki form is that of two twin katanas, shorter than the original, but with the same design.
In his human form, Yukine appears as a youthful teenager with short, messy hair. His hair is colored gold both in the anime and manga colorations. However, his eyes are reddish-orange in the anime and a yellow-amber in the manga.
He is shorter than both Yato and Hiyori. His height is 147.4cm (or 4'10") according to the Animation Visual Book released for the anime. Upon his first summoning, Yukine wears a simple white robe, resembling a Japanese shinishozoku. He is later depicted with a blue hoodie, loose grey jeans, and teal patterned knit cap.
Later on, he changes his attire to a white T-shirt, dark blue jeans, and a green knee-length jacket with a fur-trimmed hood. While as the manga progresses, his outfits are not always consistent and vary to all sorts given to whatever he is depicted with.
Yukine's hair becomes black and he grows black claws while in his new form as Hagusa. 
Yukine is first portrayed as being a bit cold and cruel. He is clearly upset and annoyed at the fact that he died, and became Yato's weapon, complaining about staying with someone like him. As a result of this and the fact that people cannot see him well, Yukine takes advantage of this and other people, stealing money, clothes, and even betraying Hiyori. Yukine though seems to feel jealous of others who are alive, upset about the fact that he is dead, and cannot make friends and learn what other students do. By then, he felt entitled to the pleasures of existing more-so than the living. He is also apparently afraid of the dark. When Yato is forced to punish Yukine through Ablution, Yukine confesses all of his sins and apologizes sincerely, and escapes the temptation that hurts Yato as his Shinki. Yukine is visibly more upbeat after his punishment, befriending Hiyori more and requesting to learn what she does in school. Yukine also is more diligent in his work as Yato's Shinki, working part-time for Daikoku to earn money for the two of them.
Despite this, Yukine is still a bit sarcastic and occasionally yells at Yato when he is upset, especially after one of his few friends, Suzuha, dies. When Yato was missing, Yukine started to be more reserved, refusing to worry about Yato, as to suppress his feelings so he wouldn't hurt Yato via negative feelings. He instead busied himself learning how to be a better Shinki from Kazuma and tutoring from Hiyori. This shows that although Yukine still holds true to his sarcastic and edgy personality, he remains incredibly compassionate for those he forms bonds with. It has been shown many times how insecure Yukine truly is especially when the subject of Nora comes up. Despite being Yato's Blessed Shinki, he felt inferior to Nora and was jealous of her because she had been Yato's Shinki for much longer than him and even knew Yato's real name before he learned of it. He was relieved when he saw Yato release Nora as his Shinki. As his Lead Shinki, Yukine has shown to be very strict with Yato especially after Yato's declared his resolve to change his ways. Yukine's methods of dealing with Yato came off as harsh but it was for Yato's future that he treated Yato in such ways.
Yukine also shows a great concern towards Yato as when he knew that the sorcerer is Yato's father and he is his lifeline, he told Yato not to kill him and told him not to meet Kazuma again and he is now their enemy as he got information about the sorcerer from Yukine by force. He also urged him to fight Bishamonten and stop her when she was fighting with Fujisaki. Yukine is somehow so jealous, as he was shocked when he saw Yato with Kazuma and didn't accept that Yato used another shinki and mentioned that he is the only Yato's shinki while talking to Nora. He also was foolish and an easy victim to manipulate, This was shown when Fujisaki told him to come and he will take care of him and he won't abandon him like Yato did, Deceived by these words he went to Fujisaki and asked him to make him his shinki.
After becoming Fujisaki's shinki, Yukine became so determined that he wanted to know everything about his life before death, but he was terrified and shocked when he knew he hadn't a life nor a family as he imagined and he was abandoned by his mother and sister, and he was killed by his father. This lead Yukine to be disappointed. On the other hand, Yukine becomes so determined that he wants to meet his father again to know why he killed him. He also shows no more interest in Yato and attacked him without any lenience believing that he abandoned him even when Yato apologized to him for doing that and he was his only shinki.
Skills and Abilities
Yukine is a very powerful Shinki. He was able to create a Boundary on his first try which Yato commented was unheard of. Even Kazuma had to practice for a long time before he was able to create a decent Boundary. He's strong enough to warrant Ebisu and Yato's father's attention and praise to the point where they've both announced their desire to claim Yukine as their own Shinki. Yato becomes worried about the latter's intentions and suggests that he and Yukine move to his small plot of land in Takamagahara.
- Rend (Zan): is a skill he obtains as Yato's sacred weapon Sekki. When Yato uses Rend, he is able to slay and exterminate phantoms.
- Severance (Zetsu): is a skill he obtains as Yato's sacred weapon Sekki. When Yato uses Severance, he is able to cut off the bonds between a human and things/other people. He uses this skill to sever the bonds between Yusuke Urasawa and Kofuku.
- Boundary (Kyoukai 境界): is an ability Shinki are available to use. Using his fingers, Yukine can draw a line and create a "boundary line" that prevents any gloom from coming past it, which is one of his only defensive mechanisms.
- Restraint (Baku 縛): Yukine has the ability to cast a binding restraint on a target. This ability appears to take the form of invisible chains. According to Daikoku, only Hafuri Vessels (such as Yukine and Kazuma) can use this ability. This ability greatly affects the other Shinkis that are not Hafuri Vessels because of superiority. Nevertheless, when a Hafuri Vessel loses his confidence and has much insecurity; like when Yukine was almost defeated by Kugaha, they can also be defeated in a boundary battle.
- Spell/Chant/Song: A skill that he obtained from his training with Kazuma. It enables him to cast spells that can be used as a protection or to attack; for example, a song Yukine used in dousing the flames in the manga. It can also summon spirits like Nora used in the manga.
- Yukine's names, Yuki (雪?) means "snow" while Yukine (雪音?) means "the sound of the snow".
- Yukine has a phobia of night and dark rooms, probably due to having his final moments being suffocated in a refrigerator in his human life.
- It is possible that the reason as Sekki, the bandages on the hilt are associated with his past life. There is a single frame in Yukine's memories where an arm is seen with bandages all over the place.
- Both Yukine and Kazuma are the only known Hafuri Vessels. In this case, Yukine changed from being an Ōdachi to a katana and wakizashi.
- His character song is Catch Ball which was sung by his voice actor.
- Hiyori guesses in Chapter 13 and Episode 1 of Noragami Aragoto, judging by his education level, that he died in his second year of middle school.
- He is very sensitive to his short height.