"Dandadan" centers around Momo Ayase, a high school girl who believes in ghosts but scoffs at the idea of aliens, and her classmate Okarun, who is convinced of extraterrestrial life but dismisses the supernatural. Their opposing beliefs lead to a bet: Momo agrees to visit a reputedly haunted location to prove ghosts exist, while Okarun ventures to a UFO hotspot to validate his alien theories. However, both encounters turn out to be far more real and dangerous than either anticipated.

Momo’s visit to the haunted tunnel results in her encountering a malevolent spirit, while Okarun’s trip to the UFO site brings him face-to-face with an alien entity. These experiences force the two to confront the reality that both ghosts and aliens coexist in their world, often intertwined in bizarre and perilous ways. As they delve deeper into these supernatural and extraterrestrial phenomena, Momo and Okarun form an unlikely partnership to navigate the chaos unleashed by their discoveries.

The narrative explores their growing bond as they face increasingly bizarre and dangerous situations, including battles with vengeful spirits, alien invasions, and otherworldly creatures. Along the way, they encounter allies and adversaries, each with their own connections to the supernatural or extraterrestrial. The story balances action, humor, and emotional moments, with a focus on the evolving dynamics between Momo and Okarun as they learn to trust each other and confront their fears.

Themes of belief, skepticism, and the unknown are central to the plot, as the characters grapple with the realization that the world is far stranger than they imagined. The series blends elements of horror, science fiction, and comedy, creating a unique tone that keeps the narrative engaging and unpredictable. Momo’s pragmatic yet courageous personality contrasts with Okarun’s awkward but determined demeanor, making their partnership a driving force in the story. Together, they uncover secrets about the supernatural and extraterrestrial forces at play, all while navigating the challenges of their everyday lives.