"Sankaku Opera" is a manga series that blends elements of mystery, psychological drama, and supernatural intrigue. The narrative centers around a high school student named Akira, who becomes entangled in a bizarre and dangerous game orchestrated by a mysterious organization known as the Triangle. This group operates in the shadows, manipulating individuals through a series of twisted challenges that test their mental and emotional limits.

Akira's life takes a drastic turn when he receives an invitation to participate in the Triangle's game. Initially skeptical, he is drawn in after witnessing the disappearance of a classmate who refused to comply. The game involves solving cryptic puzzles and completing tasks that often require participants to confront their deepest fears and moral dilemmas. As Akira progresses through the challenges, he encounters other players, each with their own motivations and secrets. Among them is Rina, a enigmatic girl who seems to know more about the Triangle than she lets on, and Kaito, a rival player whose aggressive tactics add tension to the competition.

The stakes of the game are high, with failure resulting in severe consequences, including death or permanent psychological damage. As Akira delves deeper, he uncovers the Triangle's true purpose: to identify and recruit individuals with exceptional mental resilience and strategic thinking. The organization's ultimate goal remains shrouded in mystery, but it becomes clear that they wield significant influence and resources, capable of manipulating events on a large scale.

Throughout the series, the narrative explores themes of trust, survival, and the nature of human behavior under extreme pressure. Akira's relationships with other players evolve, forming alliances and rivalries that are constantly tested by the game's demands. The story is punctuated by unexpected twists and revelations, keeping the tension high and the reader engaged. As Akira gets closer to the truth about the Triangle, he must decide how far he is willing to go to survive and whether he can maintain his humanity in the face of the organization's manipulations.