Chihaya Tomoda is a ghost who resides within Korai House, the apartment building where much of Punch Line takes place. Before her death, she was a resident of the same building, and her lingering spirit is bound to the premises, unable to move on to the afterlife. Her background as a former occupant gives her a natural familiarity with the apartment's layout and history, which she uses to guide the living characters.

In terms of personality, Chihaya is gentle, kind-hearted, and notably shy. She lacks the menace or tragedy typically associated with ghosts in fiction, instead presenting herself as a soft-spoken and slightly melancholic presence. Her demeanor is polite, and she often seems apologetic for her situation or for startling the living. Despite being invisible to most people, she tries to be helpful, though her limited ability to interact with the physical world often frustrates her quiet efforts.

Chihaya's primary motivation is to protect the protagonist, Yuta Iridatsu, who possesses the unique ability to see and hear her. She develops a deep emotional connection to Yuta, feeling both grateful for his attention and sorrowful that they exist in different planes of reality. Her actions are largely driven by a desire to keep him safe from the escalating supernatural and apocalyptic threats surrounding Korai House. There is a romantic undercurrent to her feelings, as she cares for him in a way that surpasses mere friendship or obligation, yet she remains reserved about expressing it fully due to her ghostly state.

Within the story, Chihaya serves as Yuta's initial guide and confidante, explaining some of the basic rules of his unusual situation, such as his tendency to cause catastrophe if he gets too excited. She is the emotional anchor in the chaotic environment, often representing the human stakes of the plot. Her role evolves from a passive observer to an active participant as the narrative explores the nature of her death and her unresolved attachments to the world.

Her key relationships center on the other residents of Korai House. Her bond with Yuta is the most significant, acting as the emotional core that influences many of his decisions. She also interacts with the other female residents, though from a distance, as they cannot see her. Chihaya harbors a particular awareness of the magical girl Mikatan, feeling a mix of admiration and concern. Her relationship with the elderly ghost that also haunts the building is more antagonistic or wary, as the older spirit has its own ambiguous agenda.

Chihaya undergoes subtle but meaningful development throughout the series. Initially portrayed primarily as a helpless spirit, she gains agency as the secrets of the apartment and the catastrophe countdown are revealed. She confronts the circumstances of her own past and death, which allows her personality to grow from purely passive to courageously active. This development is tied to her accepting her situation rather than merely lamenting it, ultimately leading her to take decisive actions that affect the fate of the group.

Regarding notable abilities, Chihaya can become selectively invisible and intangible to the living, allowing her to pass through walls and objects. However, her spiritual energy is limited. Her most remarkable ability is a form of temporary possession or ghostly influence, which she can use to manipulate small objects or, in rare cases, briefly become visible to others. She is also capable of sensing spiritual disturbances and the flow of destiny, giving her insight into the impending disasters. Her powers are generally weak compared to the more overt spiritual phenomena in the series, which underscores her character as a fragile but determined presence.