"Koyomimonogatari" is a 12-episode anime series that serves as a prequel and interquel to the larger Monogatari franchise. Each episode is a short, self-contained story, typically around 10 minutes long, focusing on Koyomi Araragi, the series' protagonist, and his interactions with various characters across different points in time. The narrative is structured around a calendar format, with each episode corresponding to a specific month, spanning from April to March of the following year.

The series begins in April, with Araragi encountering a mysterious stone monument in his schoolyard. This monument, which appears to be a fragment of a god, sets the tone for the episodic nature of the series, as each month brings a new supernatural or philosophical dilemma. In May, Araragi meets a young girl named Sodachi Oikura, who challenges him with a series of mathematical puzzles, hinting at deeper unresolved issues between them. June sees Araragi assisting his girlfriend, Hitagi Senjougahara, in a seemingly mundane task that reveals her pragmatic and calculating nature.

July introduces a lighter tone, with Araragi and his younger sister, Tsukihi Araragi, engaging in a playful yet eerie conversation about immortality and the nature of existence. August shifts focus to Shinobu Oshino, Araragi's vampire companion, as they discuss the concept of time and the consequences of their shared bond. In September, Araragi interacts with Nadeko Sengoku, a former classmate, in a brief but unsettling encounter that underscores her growing detachment from reality.

October features a conversation between Araragi and Tsubasa Hanekawa, his close friend, as they reflect on their past and the complexities of their relationship. November brings a confrontation with Yotsugi Ononoki, an emotionless doll-like entity, who challenges Araragi's understanding of justice and morality. December sees Araragi revisiting his past encounters with supernatural entities, tying together threads from earlier arcs in the Monogatari series.

The final episodes, set in January, February, and March, build toward a climactic revelation. In January, Araragi meets a mysterious figure who warns him of an impending threat. February deepens the mystery as Araragi uncovers a hidden shrine and learns of a ritual that could alter his fate. The series concludes in March with a dramatic confrontation that reshapes Araragi's understanding of his role in the supernatural world and sets the stage for future events in the Monogatari timeline.

Throughout "Koyomimonogatari," the narrative explores themes of time, memory, and identity, often through dialogue-heavy interactions that delve into the philosophical underpinnings of the Monogatari universe. The series serves as both a standalone exploration of Araragi's character and a bridge connecting earlier and later arcs in the franchise.