"Fūto Tantei" is a manga series that serves as a sequel to the popular "Kamen Rider W" franchise, blending elements of detective fiction with superhero action. Set in the fictional city of Fūto, the story revolves around the partnership between private detective Shotaro Hidari and his assistant, Philip, who together transform into the dual-identity hero Kamen Rider W. The narrative begins with the duo continuing their mission to protect Fūto from the threats posed by Dopants, individuals who use Gaia Memories—mysterious devices that grant superhuman abilities but often corrupt their users.

The central plot follows Shotaro and Philip as they investigate a series of interconnected cases involving Dopants, uncovering a larger conspiracy tied to the distribution and misuse of Gaia Memories. Their investigations frequently bring them into conflict with the Sonozaki family, a powerful organization responsible for producing and distributing these dangerous devices. As the story progresses, the detectives face increasingly formidable adversaries, including new Dopants with unique abilities and motivations, while also delving into the origins of the Gaia Memories and their connection to Fūto's history.

Key characters include Shotaro Hidari, a self-proclaimed "hard-boiled" detective with a strong sense of justice, and Philip, a highly intelligent but enigmatic young man with access to the Gaia Library, a metaphysical repository of knowledge. Their partnership is central to the narrative, with their contrasting personalities and skills complementing each other in both detective work and combat. Other significant characters include Akiko Narumi, the daughter of Shotaro's late mentor, who often provides comic relief but also plays a crucial role in supporting the duo, and Ryu Terui, a police officer and fellow Kamen Rider who occasionally assists in their missions.

The manga expands on the lore of the "Kamen Rider W" universe, introducing new characters, organizations, and mysteries while maintaining the core themes of justice, partnership, and the consequences of power. The episodic structure of the cases allows for a mix of standalone stories and overarching plotlines, creating a balance between action, mystery, and character development. "Fūto Tantei" appeals to fans of the original series while also offering a fresh perspective on the world of Fūto and its inhabitants.