"Beach de Q" is a manga series that centers around a group of high school students who find themselves entangled in a series of mysterious and supernatural events during a summer vacation at the beach. The protagonist, a reserved and observant student named Haruto, accompanies his classmates to a remote coastal town for a summer trip. The group includes his childhood friend, the cheerful and outgoing Aoi, the enigmatic and aloof Riku, and the studious and cautious Yuna. Their vacation takes an unexpected turn when they stumble upon an abandoned seaside inn rumored to be haunted.

As the group explores the inn, they uncover strange occurrences tied to a local legend about a cursed artifact known as the "Q Stone." According to the legend, the stone grants immense power but at a great cost, and its presence has brought misfortune to the town for generations. The students soon realize that the stone is not merely a myth when they begin experiencing vivid, shared dreams and visions of the past, revealing the tragic history of the artifact and its connection to the inn.

The narrative delves into the psychological and emotional struggles of the characters as they grapple with the stone's influence. Haruto, initially skeptical, becomes increasingly drawn into the mystery, driven by a desire to protect his friends. Aoi's optimism is tested as she confronts the darker aspects of the legend, while Riku's mysterious behavior hints at a deeper connection to the stone. Yuna, ever the rational thinker, attempts to unravel the logical explanations behind the phenomena but finds herself questioning her own beliefs.

As the story progresses, the group uncovers the truth about the Q Stone and the tragic fate of those who sought its power. The curse manifests in increasingly dangerous ways, forcing the characters to confront their fears and insecurities. The climax revolves around their efforts to break the curse, culminating in a tense and emotional resolution that ties together the themes of friendship, sacrifice, and the consequences of unchecked ambition. The series balances supernatural suspense with character-driven drama, creating a compelling narrative that explores the interplay between human emotions and otherworldly forces.