"3x3 Eyes: Genjū no Mori no Sōnansha" is a manga series that expands on the universe of the original "3x3 Eyes" story, focusing on the mystical and supernatural elements that define the franchise. The narrative centers on Yakumo Fujii, a young man who becomes entangled in the world of the Sanjiyan, a race of immortal beings with three eyes. Yakumo's life changes irrevocably when he encounters Pai, a Sanjiyan seeking to regain her humanity. After a tragic incident, Yakumo is cursed with immortality, bound to Pai as her protector until she can become human again.

The story delves into their journey through a world filled with demons, ancient rituals, and hidden powers. Yakumo and Pai face numerous adversaries, including other Sanjiyan and powerful supernatural entities, as they search for the means to break Pai's curse. The series explores themes of immortality, identity, and the cost of power, with Yakumo struggling to reconcile his human emotions with his newfound immortal existence. Pai, on the other hand, grapples with her dual nature as both a compassionate being and a powerful Sanjiyan.

The plot is driven by their quest to uncover the secrets of the Sanjiyan and the mystical artifacts tied to their race. Along the way, they encounter allies and enemies, each with their own motivations and connections to the supernatural world. The series maintains a balance between action-packed sequences and moments of introspection, highlighting the characters' growth and the complexities of their relationships. The narrative is rich with lore, blending Eastern mythology and fantasy elements to create a cohesive and immersive world.