Yuien emerges as the central protagonist, initially a troubled young man whose encounter with the Buddhist monk Shinran sparks a profound transformation. He becomes Shinran's disciple, embarking on a journey marked by both joy and heartbreak that fundamentally shapes his understanding and growth.

His past includes deep bonds with childhood friends Shinta and Gonpachi. Gonpachi's younger sister, Asa, shares a close, sibling-like relationship with him, grounding him within his relational world.

Following Shinran's death, Yuien steps into a critical role preserving and communicating Buddhist teachings. Alarmed by emerging doctrinal splits within Jōdo Shinshū Buddhism, he assembles dialogues and teachings from his time with Shinran into a written record: the Tannishō. This text aims to clarify uncertainties and prevent misinterpretations among practitioners, showcasing his dedication to maintaining Shinran's insights.

Yuien organizes the Tannishō thematically. Early sections concentrate on Shinran's core teachings regarding Jōdo Shinshū practice, the nembutsu, and Amida Buddha. Later sections confront perceived heretical views, employing Shinran's own words to correct doctrinal errors, demonstrating his structured approach to preserving theological accuracy.

A personal preface expresses his humility and deep concern over deviations from Shinran's transmitted teachings. It states his motivation: recording Shinran's spoken words while still vivid in his memory, solely to prevent potential uncertainties among fellow devotees, underscoring his role as a faithful chronicler.

Historical and narrative portrayals trace his evolution from a spiritual seeker to a committed disciple, culminating in his role as an authoritative transmitter of Buddhist teachings through his written work. His foundational relationship with Shinran influences his entire personal journey and his lasting contribution to religious preservation.