Rikka Takanashi, a high school freshman, suffers from "chūnibyō," a condition where individuals, typically adolescents, believe they possess supernatural powers or are destined for extraordinary lives. Rikka adopts the persona of the "Wicked Eye," wearing an eyepatch and carrying a black umbrella, which she claims is a magical weapon. Her behavior stems from the trauma of her father's death, as she retreats into a fantasy world to cope with her grief.

Yūta Togashi, a classmate, once experienced chūnibyō himself, adopting the alias "Dark Flame Master" during middle school. Embarrassed by his past, Yūta attempts to leave his delusions behind and start anew in high school. However, his efforts are complicated when Rikka discovers his old journal detailing his chūnibyō fantasies. Intrigued, Rikka latches onto Yūta, believing him to be a kindred spirit. Despite his initial reluctance, Yūta becomes drawn into Rikka's world, forming a bond with her and her eccentric group of friends.

The group includes Shinka Nibutani, a former chūnibyō sufferer who now strives for normalcy, and Kumin Tsuyuri, a laid-back upperclassman who indulges in naps and occasionally participates in their antics. Sanae Dekomori, Rikka's self-proclaimed "vassal," also embraces chūnibyō, often engaging in playful rivalries with Nibutani. Together, they navigate the challenges of adolescence, blending moments of humor, fantasy, and emotional depth.

As the story progresses, Yūta and Rikka's relationship deepens, with Yūta gradually helping Rikka confront her unresolved feelings about her father's death. The series explores themes of identity, growing up, and the fine line between escapism and reality. While the chūnibyō antics provide comedic relief, the narrative also delves into the characters' vulnerabilities, portraying their struggles with self-acceptance and the transition from childhood to adulthood. The interplay between fantasy and reality remains central, as the characters learn to balance their imaginative worlds with the demands of everyday life.