Art is the younger half-sister of the series' protagonist, Hazuki. Born to a different mother, she is a vampire who first appears as an antagonist driven by a deep-seated jealousy. Her full name is Artemis, though she is frequently called Arte for short.

Art's personality is largely defined by her resentment toward her older sister. She envies the attention and dedication that her family, particularly their father, showers upon Hazuki. This intense jealousy fuels her primary motivation: to deprive Hazuki of everything and everyone she truly cares for. Arte is determined to take what Hazuki values by force or to destroy it completely, making her a significant emotional and physical threat.

In the story, Art is introduced as a rival to Hazuki, often accompanied by her guardian, a vampire named Vargus or Balgus. Her role evolves from that of a jealous antagonist to a more complex figure. Despite her initial hostility, her character undergoes development when her guardian perishes. In the series finale, she is taken into the Morioka family. It is at this point that Kouhei Morioka, Hazuki's companion, manages to reach out to her. Through his influence, she is convinced to open up to a new life with caring friends and family, leaving her previous destructive path behind.

Her key relationships are primarily with her sister Hazuki, defined by rivalry and envy, and with Kouhei, who ultimately becomes the person to help her find redemption and a new home. She also shares a strong bond with her guardian, whose death is a turning point for her character.

Art possesses notable vampiric abilities, most specifically identified as being a Shadow User. This power allows her to manipulate her own shadow in various ways. She can transform her shadow into a weapon, most commonly a scythe. She can also mold it into a replica of herself, creating a doppelganger to fight or distract her enemies.