"To Your Eternity" centers on an immortal being known as Fushi, created by a mysterious entity to observe and learn from the world. Initially taking the form of a rock, Fushi evolves into a wolf after encountering a dying boy in a snowy wilderness. Through this transformation, Fushi gains the ability to take on the forms of those it encounters, absorbing their memories and emotions. The narrative explores Fushi's journey as it interacts with various individuals and cultures, grappling with the complexities of human existence, mortality, and the passage of time.

The story begins with Fushi's bond with the boy, who teaches it basic human concepts like language and emotion. After the boy's death, Fushi continues to wander, encountering a young girl named March and her village. Tragedy strikes again when March and her people are killed, leaving Fushi to carry their memories. As Fushi travels further, it meets other characters, including Parona, a skilled warrior, and Gugu, a boy with a disfigured face who becomes a close companion. Each encounter shapes Fushi's understanding of humanity, as it learns about love, loss, and the inevitability of death.

A recurring antagonist, the Nokkers, emerges as a threat to Fushi and those it cares about. These shadowy entities seek to destroy Fushi, forcing it to defend itself and its companions. Over time, Fushi's abilities grow, allowing it to take on multiple forms and wield powerful weapons. However, its immortality becomes a source of isolation, as it outlives those it forms bonds with, leading to profound emotional struggles.

The narrative spans centuries, with Fushi witnessing the rise and fall of civilizations and the evolution of human society. Key characters like Hayase, a relentless pursuer of Fushi, and Tonari, a determined girl who aids Fushi in its battles, play significant roles in its journey. The series delves into themes of identity, purpose, and the cyclical nature of life, as Fushi seeks to understand its place in the world and the meaning of its existence.

"To Your Eternity" is a poignant exploration of the human condition through the eyes of an immortal being, blending moments of heartbreak and hope as Fushi navigates an ever-changing world. The story's episodic structure allows for a diverse range of characters and settings, each contributing to Fushi's growth and the overarching narrative.