"Needless" is set in a post-apocalyptic Japan, divided into the Black Spot, a devastated area contaminated by a mysterious explosion, and the City, a controlled and prosperous region. The Black Spot is inhabited by individuals known as Needless, who possess supernatural abilities referred to as "Fragments." These abilities range from elemental manipulation to enhanced physical prowess, making Needless both feared and hunted by the government and corporations seeking to exploit their powers.

The narrative centers on Adam Blade, a brash and powerful Needless with the ability to copy other Fragments. Blade operates as a vigilante, protecting the weak and fighting against the oppressive forces of the Simeon conglomerate, which seeks to capture and experiment on Needless. Blade’s journey intertwines with Cruz Schild, a young boy who becomes his reluctant companion after being saved from Simeon’s forces. Cruz, though initially powerless, proves resourceful and gradually becomes integral to Blade’s mission.

The story delves into the conflict between Blade and Simeon, led by the enigmatic and ruthless Arclight, who wields immense power and harbors a personal vendetta against Blade. Arclight’s subordinates, a group of elite Needless known as the "Simeon’s 12 Apostles," serve as recurring antagonists, each possessing unique and formidable Fragments. The series explores themes of power, morality, and survival as Blade and his allies confront Simeon’s forces, uncovering secrets about the Black Spot’s origins and the true nature of Fragments.

Key characters include Eve Neuschwanstein, a young girl with healing abilities who joins Blade’s group, and Disk, a scientist with a mysterious past who aids the protagonists. The dynamic between Blade’s team and Simeon’s Apostles drives much of the action, with battles showcasing creative uses of Fragments and strategic confrontations. The series balances intense fight sequences with moments of humor and camaraderie, particularly through Blade’s over-the-top personality and Cruz’s grounded perspective.

As the plot progresses, revelations about the Black Spot’s history and the origins of Fragments come to light, tying the characters’ fates to the larger mystery of the apocalypse. The narrative builds toward a climactic showdown between Blade and Arclight, with the fate of the Black Spot and its inhabitants hanging in the balance. "Needless" combines action, science fiction, and post-apocalyptic elements, offering a story that is both fast-paced and layered with intrigue.