Mutsumi Kuonji lives in a town where supernatural events are commonplace, including the regular sight of a flying whale observing the streets below. His daily routine involves navigating school life and interacting with a circle of friends possessing unusual traits: Sae Nagumo (known as Sacchan), Nina, and an entity named Allen. These social encounters often spiral into comedic or ecchi complications, frequently involving exposed undergarments or beach excursions.

A pivotal part of Mutsumi's past is a childhood promise made with Sacchan. They agreed to meet again at a specific spot, but Mutsumi failed to appear. Years later, while traveling to school, he passed through the same location and spotted Sacchan, who had waited there continuously since their original agreement. This reunion rekindled their friendship and shared activities, though the longevity of this renewed connection is indicated as potentially finite.

Mutsumi's experiences unfold in an environment where extraordinary occurrences, like the persistent aerial whale, are accepted as normal. The whale's presence connects to wider supernatural phenomena within the town, phenomena that remain largely unexplained throughout his documented experiences.