"Watashitachi no Mirai" centers on a group of high school students navigating the complexities of adolescence while grappling with a mysterious phenomenon that intertwines their futures. The narrative begins with the protagonist, Haruto, a reserved yet observant student, who discovers an old, enigmatic device in his school’s storage room. Upon activating it, he and his close-knit group of friends—Yuna, a spirited and empathetic classmate; Riku, a pragmatic and tech-savvy peer; and Aoi, a thoughtful and introspective artist—are thrust into a series of visions depicting their potential futures. These glimpses are fragmented and often contradictory, revealing both hopeful and harrowing outcomes.

As the group delves deeper into the origins of the device, they uncover its connection to a long-forgotten school legend about a "Future Mirror" capable of revealing one’s destiny. The visions grow more intense, forcing the characters to confront their fears, insecurities, and unresolved conflicts. Haruto, for instance, sees a future where he becomes estranged from his friends, while Yuna witnesses a version of herself sacrificing her dreams for the sake of others. Riku’s visions highlight his struggle with self-doubt, and Aoi’s reveal her fear of losing her creative spark.

The story explores themes of choice, consequence, and the fluidity of destiny. The characters must decide whether to accept the futures they see or actively work to alter their paths. Their decisions are complicated by external pressures, such as familial expectations, societal norms, and the unpredictable nature of their relationships. The narrative builds tension as the group realizes that their actions in the present have ripple effects, not only on their own lives but also on the lives of those around them.

As the series progresses, the line between reality and the visions blurs, leading to moments of introspection and growth for each character. The climax revolves around a pivotal event that forces the group to make a collective choice, determining whether they will embrace the uncertainty of the future or cling to the safety of the present. The resolution ties together the emotional arcs of the characters, offering a nuanced exploration of how they reconcile their aspirations with the realities of their lives.