Ōima, inspired by her own grandmother's death, aimed to write about survival and the character Fushi, who initially is an emotionless stone but gradually develops a self and personality as a result of interacting with humans.

Critical response to the series debut was very positive, based on the emotional focus on the villagers and Fushi to the point of often earning perfect scores.

Fushi's continuous character arc was praised while Ōima's artistry enjoyed critical acclaim due to its detailed facial expressions and environments.

An otherworldly being called the Beholder creates a white orb (later named Fushi by a rambunctious young girl).

He travels to the land of Ninannah, and meets a young girl called March, who was chosen as a sacrifice to a large white bear named Oniguma.

Hayase pays a girl named Tonari to lure Fushi and Pioran onto a prison ship to Jananda island.

For the next two centuries, Fushi avoids extensive human contact, and is regularly visited by the obsessed Hayase's reincarnations and descendants; one of which is a male named Kahaku.

After awakening five centuries into the modern era, Fushi resurrects the eleven spirits following him, including his closest friends March, Gugu, Tonari Dalton and Bonchien.

Before losing his memories Satoru reveals that he created the world out of boredom, then wanted to die in his creation, leaving Fushi to watch over it.

The decision to give the manga a fantasy setting was taken for the freedom it afforded, with supernatural beings offering unusual possibilities.

There are approximately 13 characters that are greatly affected by Fushi and which, before the series' beginning, would lead Ōima to the title, "Ash Swords of 13 People" (『13人の灰剣』), before being replaced by "To Your Eternity".

For research, she watched several documentaries in order to learn how to make the boy look like he was living in a world of "survival", with limited resources and skills.

[22] Director Masahiko Murata [ja] expressed surprise when first reading the manga series, initially believing the young villager would be the lead character rather than Fushi.

Murata stated that, as minor parts of the manga were changed, the anime would stay true to the original printed version.

[23] The official Twitter account of the anime series stated that the main theme presented through March (and later Fushi) was the notion of growing into adulthood.

Kawashima thought his character to be exhausting based on his varied experiences, while Tsuda felt Fushi was too mysterious.

[25] For the sixth episode, Kawashima expressed difficulty portraying Fushi's lines due to the fact that the character was learning how to speak.

[26] Ryoko Shiraishi commented that while she enjoyed voicing Gugu, the character's fluid personality made the work more challenging.

[37] On January 8, 2020, Kodansha announced that the manga would receive an anime television series adaptation, to air on NHK Educational TV.

[51] In 2018, Ōima won the Daruma de la Meilleure Nouvelle Série at the Japan Expo in Paris, France for To Your Eternity.

[56] The manga's narrative and setting have been praised by critics like Otaku USA due to its multiple fantasy and drama elements.

However, he felt the story provided in the first volume lacked the emotional impact from the mangaka's previous work, A Silent Voice.

[60] As the manga progressed, Fushi's character arc was the subject of praise as he was closer to acting like a human in contrast to his nearly emotionless introduction.

[61][62][63] Manga News furthermore enjoyed the series' time-skips as Fushi's immortality allowed him to blend in with newer, more modern scenarios.

IGN listed it among the best anime series of Spring 2021, directing readers to its portrayals of Earth's culture but refrained from further explaining the premise to avoid spoilers.

[73] Three ANN writers gave the anime's premiere a perfect score, based on the emotional storytelling involving Fushi and the nameless youth, most notably when the latter, initially cheerful and talkative, quickly becomes filled with despair, as he cannot find any other people in the region.

[74] Similarly, The Fandom Post gave the series' premiere a perfect score despite having read the manga years before, based on the cast's performances and Utada Hikaru's theme song "Pink Blood" which helped to convey a moving story.

[76] Comic Book Resources felt the adaptation series was well done and given an appealing soundtrack as the emotional scenes became stronger thanks to the music provided.

[77] Critics praised the bonding involving Fushi, March and Parona, noting how heroic they were for each other while providing opportunity for more entertaining scenes.

[79][80] Fushi's increasing display of humanity was praised, with the sixth episode giving him enough screentime to become the sole main character.