Character Arc
Yukine is a wandering spirit of a young person who died before his time and is taken in by Yato to become his Regalia, a spirit that gods transform into weapons. Yato names him and wields him in his form as a blade, giving Yukine a purpose and a place to belong. Resentful at first about his lost life and the rules of his new existence, Yukine struggles to accept being bound to a poor, demanding god.
His bitterness and small acts of rebellion begin to physically harm Yato, since a Regalia's misdeeds sting and corrupt their master. This leads to one of the series' most emotional storylines, in which Yukine's blight nearly destroys Yato and forces the people around them to intervene. Confronting the pain he has caused becomes the turning point that pushes Yukine toward maturity.
As the series progresses, Yukine grows from a sullen, troubled boy into a loyal and capable partner who takes pride in serving Yato well. He learns to channel his feelings rather than lash out, eventually becoming a stronger and more trusted Regalia. His arc is a coming-of-age story about grief, responsibility, and finding family with Yato and Hiyori after everything he lost in life.