An Orb, known only as It, is cast to Earth to be observed from afar. Capable of changing forms from beings whose reflections It captures, It first becomes a rock and then, due to the rising temperature, moss. It does not move until one snowy day, a wolf at death's door barely crosses by. When It takes the animal's form, It attains awareness of its consciousness and starts to wander with an unclear destination in mind. Soon, It comes across the wolf's master—a young boy waiting for his tribe to return from a paradise abundant with fish and fruit in the south. Though lonely, the boy still hopes his loved ones remember him and that he’ll reunite with them someday. The boy leaves home with It to find paradise using his tribe’s traces. However, with a heavily injured body and no sight of his elder comrades, what will become of the boy? To Your Eternity illustrates the story of an immortal being experiencing humanity, meeting all types of people in many places throughout time.

After seeing enough death and tragedy, the immortal Fushi secludes himself on an island, defending himself from enemy Nokkers. However, instead of attacking Fushi in isolation, Nokkers begin targeting the settlements outside of his reach in hopes of luring him out. Soon, a group known as the Guardians—led by Hisame, the descendant of the deceased warrior Hayase—finds Fushi. Inspired by how Fushi protected Janada Island from the Nokkers years ago, the Guardians have grown a considerable following and are recognized throughout the world. Initially reluctant, Fushi allows the Guardians to accompany him to the site of the Nokkers' recent attack. In their village, Fushi meets a few valuable allies, both new and old. But as the conflict with the Nokkers only leads to more loss, Fushi must find the inner strength to face his inevitable sorrow.

Following the battles in Renril, Fushi, like a tree, spreads his roots throughout the world, fighting to eliminate the Nokkers. Hundreds of years later, having completed his mission, he awakens in the modern era. He enjoys a life of peace, free of enemy threats and surrounded by precious friends, new and old. But ominous shadows grow near yet again. Enemies that enter into the fissures of the mind. And Fushi learns of the true goals of his creator, the Beholder.