"20th Century Boys" is a science fiction mystery manga written and illustrated by Naoki Urasawa. The narrative spans several decades, beginning in the late 20th century and extending into the early 21st century, weaving a complex tale of friendship, conspiracy, and the struggle against a mysterious cult.

The story centers around Kenji Endo, a former rock musician turned convenience store manager, who becomes entangled in a series of events tied to a childhood memory. As children, Kenji and his friends created a fictional story about a group of heroes saving the world from an evil organization. Decades later, a cult known as the "Friends" emerges, led by a figure called "Friend," whose actions and symbols eerily mirror the fictional tale Kenji and his friends invented. The cult gains immense influence, orchestrating global catastrophes and manipulating society.

Kenji discovers that the cult's leader may be someone from his past, and he reunites with his childhood friends to uncover the truth. The narrative alternates between timelines, revealing the origins of the "Friends" cult and the events that shaped its rise. Key characters include Kanna, Kenji's niece, who becomes a pivotal figure in the resistance against the cult, and Otcho, one of Kenji's closest friends, who plays a crucial role in the fight against "Friend."

As the story progresses, the scope of the conspiracy expands, involving biological weapons, mass manipulation, and a dystopian future where the cult's influence dominates society. The manga explores themes of memory, identity, and the consequences of childhood fantasies manifesting in adulthood. The intricate plot is marked by twists, betrayals, and the enduring bonds of friendship, as Kenji and his allies strive to dismantle the cult and prevent global annihilation.

The narrative concludes with a resolution that ties together the multiple timelines and character arcs, revealing the true identity of "Friend" and the ultimate fate of Kenji and his companions. "20th Century Boys" is celebrated for its meticulous plotting, rich character development, and the seamless integration of personal and global stakes, making it a standout work in the mystery and science fiction genres.