Kanon, formally named Yoshiya, functions as a young male servant within the Ushiromiya household on Rokkenjima island. Kinzo Ushiromiya created him as "furniture," granting combat capabilities for protection due to Kinzo's concerns about his own mortality, though Kanon possesses a weaker heart than his counterpart Shannon. Physically, he appears as a frail boy with medium-length dark gray hair and blue eyes. His attire consists of a black collared shirt with a purple cravat, red shorts, striped socks, brown shoes, and a distinctive red hat.

He maintains a serious, antisocial demeanor, performing duties diligently yet mechanically. Kanon strictly adheres to the belief that furniture lacks humanity and should not experience human emotions like love. This conviction leads him to reject romantic advances from Jessica Ushiromiya despite mutual feelings, while simultaneously disapproving of Shannon's relationship with George Ushiromiya. Internally, he grapples with conflict between duty and emotion, manifesting as stoicism masking deep-seated anxiety and self-doubt, traits aligning with psychological classifications of ISTJ personality and Enneagram Type 6 ("The Loyalist").

Functionally, Kanon can manifest a red energy sword and demonstrates enhanced agility, specializing in close-quarters combat. He engages supernatural entities such as the Stakes of Purgatory and defeats Lucifer. His abilities amplify when synchronized with Shannon, as they originate from the same furniture construct; together they deploy magic interference fields capable of neutralizing threats like the Chiester Sisters' sniper attacks. Kinzo privately trained him in rifle marksmanship.

His background reveals he was raised alongside Shannon at the Fukuin House orphanage after servants Genji and Nanjo rescued him as an infant. This followed Natsuhi Ushiromiya's attempted infanticide upon discovering the child was Kinzo's illegitimate offspring through rape. As "Yasu," he developed multiple personas to cope with trauma and physical infertility, resulting in the distinct identities of Shannon (the idealized servant) and Kanon (the protective male persona).

His relationship with Jessica evolves across narratives, starting with reserved interactions and progressing to romantic acknowledgment in Dawn of the Golden Witch. He carries a spare bronchodilator for her asthma and eventually reciprocates her feelings despite his furniture complex. Kanon views Shannon as an older sister, displaying fierce protectiveness when she is threatened. A dynamic shift occurs when Kanon and Shannon duel in Episode 6, representing Yasu's internal conflict between personas; Kanon's defeat symbolizes the suppression of his identity in favor of Shannon's existence.

Within metaphysical contexts like the Witch Domain and City of Books, Kanon transcends physical limitations. Here, he utilizes conceptual weapons such as Blue Truths—theoretical arguments manifesting as stakes capable of negating an opponent's existence unless refuted by Red Truths. His existence in these realms ties to anchors like Beatrice or Ange Ushiromiya; he ceases to exist if they perish.

Kanon's narrative concludes through integration with Shannon and Beatrice into a unified entity named Clair Vaux Bernardus. This fusion occurs during the Golden Land's creation, resolving the personas' fragmented existence and fulfilling the epitaph's requirements for the inheritance.