"Owarimonogatari" is the fifth installment in the Monogatari series, adapting the final arcs of Nisio Isin's light novels. The narrative is divided into two main storylines, each exploring the past and present of the protagonist, Koyomi Araragi, as he confronts unresolved mysteries and personal dilemmas.

The first arc, "Ougi Formula," delves into a mystery from Araragi's middle school years. Araragi and Ougi Oshino, a mysterious girl claiming to be the niece of his mentor Meme Oshino, investigate the disappearance of a classroom. Through their investigation, they uncover a bizarre phenomenon tied to a student named Izuko Gaen, who manipulated the school's layout to create a hidden room. This arc reveals Ougi's enigmatic nature and her connection to Araragi's past, setting the stage for her role in the overarching narrative.

The second arc, "Sodachi Riddle," shifts focus to Araragi's childhood and his relationship with Sodachi Oikura, a former classmate. The story alternates between the present, where Araragi and Ougi help Sodachi confront her traumatic past, and flashbacks that reveal their shared history. Sodachi's family issues and her resentment toward Araragi for failing to help her during her struggles are central to this arc. The narrative explores themes of guilt, responsibility, and the lingering effects of childhood trauma.

The final arc, "Sodachi Lost," continues Sodachi's story, with Araragi and Ougi attempting to locate her after she disappears. This arc further examines Sodachi's psychological struggles and her inability to move past her pain. Araragi's efforts to reconcile with her highlight his growth as a character and his desire to atone for his past inaction.

Throughout "Owarimonogatari," the series maintains its signature dialogue-heavy style, blending supernatural elements with introspective character studies. Key characters include Koyomi Araragi, whose journey of self-discovery drives the narrative; Ougi Oshino, whose true nature remains ambiguous; and Sodachi Oikura, whose tragic backstory adds emotional depth. The series ties together loose ends from previous installments while setting up the final conflicts of the Monogatari saga.