Ayumu Aizawa is the primary protagonist of the first story arc, and his journey serves as the initial lens through which the series explores its themes of memory, self-discovery, and connection with the supernatural. He is a young boy who arrives in the quiet, rural town of Tana to spend his summer vacation at the home of his father, who works there as a veterinarian. Ayumu’s time in Tana begins with a sense of aimlessness, as he spends his days biking across the valley without any clear purpose or desire. This behavior reflects a deeper personal stagnation; he is described as a boy who does not discover anything about himself, seemingly wondering what he wants to do with his time.

In terms of personality, Ayumu presents as an emotionally distant and introverted individual, a loner who holds himself apart from others. He is a hikikomori type, characterized by his antisocial tendencies, though he is notably more active than the protagonist of the second arc, choosing to explore his environment on his bicycle rather than remaining withdrawn in a single location. His demeanor is defined by a quiet, objective outlook on the world around him.

The central motivation for Ayumu during the summer arc stems from a mysterious gap in his memory. As a child, he had previously lived in Tana, but he cannot remember the events of that summer, which is strongly hinted to be connected to a profound, supernatural experience. His discovery of a strange, ageless boy named Wakkun, who wears a raincoat and galoshes identical to those Ayumu himself wore as a child, becomes the catalyst for his search. Accompanied by Wakkun are two mysterious, flying entities of light known as Dosshiru and Shisshin. Ayumu’s journey throughout the first half of the series is driven by his need to understand his forgotten past and his unique connection to Wakkun and these light beings.

Ayumu’s role in the story is that of an observer and a participant in a supernatural mystery. He is one of the few characters who can see and interact with the material fairies, the strange spheres of light that appear in Tana and are often only visible in the reflections of animals’ eyes. A local reporter, Akira Sukawara, becomes aware of the strange phenomena and presses Ayumu for information, positioning him as a reluctant key to understanding the town’s mysteries. His most significant relationship is with Miku, a girl from Tana who knows more about the town’s secrets than she initially reveals. Together, with the help of other townspeople, they work to uncover what happened during Ayumu’s lost summer.

Ayumu’s development is marked by his transition from a state of aimlessness to one of active engagement with his past and the world around him. He begins as a passive visitor but grows through his quest to recover his memories and understand Wakkun. His significance continues beyond the first arc, as he reappears in the second arc, the Winter Arc, which takes place in Yokohama a year and a half later. By this time, he is no longer the main character but a supporting figure, now a student living in the city, showing that his summer in Tana was a formative experience that changed the course of his life.

Regarding notable abilities, Ayumu possesses the innate capacity to see and interact with the material fairies, such as Dosshiru and Shisshin, which are invisible to most ordinary people. His primary role in the narrative is not defined by physical powers but by his deep, unresolved connection to these supernatural entities and his quest for personal truth. While no specific supernatural abilities are documented for him beyond this perception, his unique childhood bond with the enigmatic Wakkun is the central ability that drives the plot forward.