Sachi Saigan, a young orphan abandoned by her parents a decade before the story begins, was raised at the Saigan Temple by a poor priest. This temple, her only home, faces destruction when the Minoura clan plans to demolish it to build a hotel. Sachi fiercely protests this act, demonstrating her deep protective attachment to the temple and its statue of the Thousand-Hand Kannon. Her defiance against the threatening gangsters reveals her determination, though she is initially powerless to stop them.

The conflict transforms dramatically when the Thousand-Hand Kannon statue unexpectedly shatters and comes to life, revealing a boy named Senju. Senju declares himself an emissary of the bodhisattva Kannon and states his mission is to find and protect the reincarnation of the future Buddha, Miroku. He identifies Sachi as this incarnation, the Maitreya Bodhisattva, destined to achieve enlightenment and save the world once Buddhist teachings are forgotten. This revelation confirms Sachi's central role as the destined successor to Śākyamuni Buddha.

Initially suspicious of Senju, Sachi gradually accepts his protection as envoys of Mara—forces seeking to corrupt with earthly desires—begin targeting her. Her journey focuses on reaching India with Senju, where she must awaken her true nature and attain enlightenment. This pilgrimage forms the core of her character arc, moving her from a sheltered orphan to a pivotal figure in a spiritual conflict.

Throughout their travels, Sachi confronts opposition not only from Mara but also from other Buddha figures who doubt Senju's ability to protect her. Her relationship with Senju evolves from wariness to reliance amidst these constant threats. The narrative centers on her destiny to re-teach the pure dharma to a world that has lost it, establishing her as a beacon of hope against escalating dangers.