Akashi Kuniyuki is a tachi sword brought to life, originally forged by Rai Kuniyuki, the founder of the Rai school of sword-making. He is a hereditary treasure of the Matsudaira clan, which once ruled over the Akashi Domain, a connection that gives him his name. Within the citadel, he considers himself the guardian of two other swords, Aizen Kunitoshi and Hotarumaru, a role he takes on due to the historical relationship between their smiths. Akashi is best known for his profound and performative lack of motivation, openly claiming that his apathy is his main selling point. He frequently speaks in a tone that makes his true feelings difficult to discern, though he occasionally reveals a serious expression that hints at hidden depths beneath his casual exterior. He shows clear favoritism toward Hotarumaru, becoming involved and motivated only when it concerns him, while being notably less attentive to Aizen Kunitoshi. His arrival at the citadel causes anxiety for Aizen and Hotarumaru, who worry that his notoriously lazy style will lead to conflict, and his behavior is initially linked to a series of mysterious incidents. His development centers on integrating into the community and forming an unconventional family unit with the other Rai clan swords, where the younger swords often find themselves looking after their apathetic elder.