"Just Because!" is a 12-episode anime series that explores the final months of high school for a group of students whose lives intertwine as they navigate relationships, aspirations, and the uncertainties of the future. The story begins with the unexpected return of Eita Izumi, a transfer student who moves back to his hometown during the third year of high school. His arrival coincides with the final semester, a time when his former classmates are already preparing for graduation and making decisions about their post-school lives.

Eita reconnects with his childhood friend, Haruto Sōma, who is focused on baseball and harbors feelings for their classmate, Ena Komiya. Ena, a photography enthusiast, is preoccupied with capturing meaningful moments before graduation. Meanwhile, Mio Natsume, a diligent student and Eita's former classmate, is preparing for university entrance exams while grappling with unresolved feelings from the past. The group is rounded out by Hazuki Morikawa, a cheerful and supportive friend who becomes a confidante for several characters.

The narrative unfolds through a series of interconnected events, with each character's decisions and emotions influencing the others. Eita's presence acts as a catalyst, prompting shifts in relationships and self-reflection among his peers. Haruto struggles to confess his feelings to Ena, while Ena herself becomes increasingly aware of her own emotions and aspirations. Mio, who shares a complicated history with Eita, finds herself revisiting past misunderstandings and reevaluating her priorities. Hazuki, though not directly involved in the romantic tensions, provides emotional support and helps bridge the gaps between her friends.

As the school year progresses, the characters face pivotal moments that force them to confront their fears and desires. The story emphasizes the fleeting nature of time and the importance of seizing opportunities before they pass. Themes of unspoken feelings, missed connections, and the bittersweet transition from adolescence to adulthood are central to the narrative. The series concludes with a sense of closure, as the characters take steps toward their futures, having grown through their experiences and interactions during this critical period of their lives.