Hikari Tsukishiro is a pale, slim teenager standing 146 cm tall and weighing 39 kg, with measurements of 74-55-76 cm. Her short white hair features spiky bangs, and her eyes are red. She typically wears a school uniform, yukata, beret, and various ribbons.

Reserved, serious, and cynical, she distances herself from others due to low self-esteem and fear of rejection, yet deeply longs for connection. An orphan and twelfth grader, she works as a shopkeeper and holds unparalleled knowledge of Kazune City's mysteries. Her skills include katana proficiency, cooking, and landscape painting focused on open skies.

She forms a pivotal bond with Makoto Okano after he rescues a cat; his hands-on nature contrasts her observational demeanor and draws her interest. Her narrative route unlocks only after completing four other characters' routes.

Hikari created Kazune City and has existed since ancient times, originally serving as a priestess. Witnessing ritual sacrifices drove her to burn a temple. Confronting the orchestrator—her brother—she learned he would escape a curse, forcing her to take his place. Consequently, she perpetuated a cycle of killing to protect the town for centuries.

Her development peaks when Makoto expresses a desire for universal happiness, prompting her confession. Overwhelmed, she attempts suicide by leaping off a cliff, but Makoto saves her. Inspired by his childhood promise to another, she performs the Doukatai ritual on herself, vanishing and reborn as Aya. Memories and records of her existence fade from those who knew her and photographs. As Aya, she encounters Makoto without full recollection of their past.

Throughout her story, her sole companion is a black cat, underscoring her isolation before bonds with Makoto and others form.