"To Your Eternity" begins with an otherworldly entity, referred to as the Orb, sent to Earth to observe and learn. Initially taking the form of a rock, the Orb evolves into a wolf after encountering a lone, injured boy in a snowy wilderness. The boy, who remains unnamed, is the last surviving member of his village and has been waiting for his tribe to return. The Orb, now in the form of the boy’s deceased pet wolf, accompanies him on a journey to find others. The boy dies shortly after, but the Orb absorbs his form and memories, gaining the ability to transform into him and retain his emotions.

As the story progresses, the Orb, later named Fushi, continues to evolve by encountering and absorbing the forms of other beings upon their deaths. Each transformation grants Fushi new abilities and deeper emotional understanding, but also burdens him with the memories and pain of those he has lost. Fushi’s journey spans centuries, taking him across diverse landscapes and cultures, where he interacts with humans, spirits, and other entities. Key characters include March, a young girl from a remote island; Parona, March’s older sister figure; Gugu, a boy with a disfigured face who becomes a close friend; and Hayase, a relentless pursuer who seeks to exploit Fushi’s immortality for her own purposes.

The narrative explores themes of mortality, identity, and the human experience, as Fushi grapples with the purpose of his existence and the weight of his immortality. Over time, Fushi faces adversaries known as the Nokkers, mysterious beings that seek to destroy him, adding a layer of conflict and urgency to his journey. The story balances episodic encounters with a larger, overarching plot, weaving together moments of joy, sorrow, and introspection as Fushi learns what it means to live, love, and lose in a world defined by impermanence.