Susukihotaru is a 16-year-old Hanyuu, born to a human mother and a spirit father. Growing up in a society viewing half-spirits as bad omens led to her abandonment as an orphan, resulting in deep-seated shyness and a fear of humans that initially prevented her from making eye contact.

She possesses a unique empathic ability: perceiving emotions, memories, and past events tied to objects or people through physical contact, which she uses during investigations. These powers awakened after meeting Zakuro, who unlocked her latent spiritual abilities, making Zakuro immensely important to her. In combat, she supports her team by chanting melodies while brandishing cherry blossom branches, key to their spiritual techniques.

Assigned to the Ministry of Spirit Affairs, she was partnered with human military lieutenant Riken Yoshinokazura. His imposing height and stoic demeanor terrified her at first. Their relationship shifted when Riken crouched to ease her fear during their initial meeting, revealing his kindness. A pivotal moment occurred when an evil sword possessed Susukihotaru, causing her to accidentally injure Riken; the physical contact during this event allowed her to sense his profound concern for her, deepening their emotional bond.

Over time, she develops romantic feelings for Riken, becoming comfortable interacting with humans and no longer looking down or avoiding eye contact specifically with him. She also firmly believes in horoscopes, consulting them as influential daily guides. Her character arc culminates in a mutual love confession with Riken, marking her transition from isolation to acceptance and emotional security.