Chiaki Nishiya, also known as Wagen-san, is a tsukumogami, a type of yōkai that awakens when an object reaches its hundredth year of service or is deeply cherished by its owners. In Chiaki’s case, the object in question is a classic Volkswagen Beetle, and his human form reflects the vehicle’s gentle and unassuming nature. He resides with an elderly man named Kazuhiko Nishiya, who was his original owner alongside his late wife. Chiaki came to life after being driven by the couple for forty years, and his awakening was triggered by the wife's passing from an illness, turning a beloved family car into a sentient, immortal being.

In terms of personality, Chiaki is portrayed as a gentle, calm, and deeply nostalgic individual. He carries a profound sense of loss and devotion, particularly regarding his deceased owner. His connection to the past is tangible, as he often reflects on the small details of his human life, such as his wife's habit of wearing brooches. He speaks of her with a quiet, enduring love, noting how accessories like her brooches were not just decorations but an integral part of her identity. This melancholy is balanced by a steadfast loyalty to Kazuhiko, with whom he now shares a quiet household, suggesting a friendship built on shared memory and mutual care.

Chiaki’s role in the story is that of a supporting character within a community where humans and supernatural beings coexist. He is part of the social circle that includes the nekomata Buchio, the tengu Jiro, and the kitsune Yuri. While not a primary protagonist, his presence enriches the series’ exploration of themes like aging, memory, and the nature of soulful connections. As a tsukumogami, he represents the idea that objects absorb the emotions and histories of those who use them, becoming living repositories of human experience. His daily life alongside Kazuhiko serves as a quiet example of how change and loss can lead to new, meaningful forms of relationship.

Throughout the series, Chiaki’s development is subtle, rooted in his adjustment to life as a yōkai while holding onto his human past. He evolves from simply mourning his wife to actively engaging with the present, finding purpose in companionship with Kazuhiko and the wider community. His key relationships are with Kazuhiko, his surviving human partner, and the other yōkai who understand his unique transition from object to person. As a tsukumogami, Chiaki’s notable abilities are tied to his origins: he can transform between his humanoid form and his original Volkswagen form, allowing him to interact with the world as either a person or a vehicle. This ability symbolizes his dual existence as both a cherished memory and a living being moving forward in time.