One's story revolves around Kouhei Orihara, the main protagonist, who suspects that at some point his current life will change while living a peaceful daily routine. Due to this, he begins to seclude himself in the Eternal World, a world within his mind. The game's main recurring motif is a focus on the Eternal World, a mystical alternate space which is never clearly explained, and the details of which are unknown.

One's story revolves around Kouhei Orihara, the main protagonist, who suspects that at some point his current life will change while living a peaceful daily routine. Due to this, he begins to seclude himself in the Eternal World, a world within his mind. The game's main recurring motif is a focus on the Eternal World, a mystical alternate space which is never clearly explained, and the details of which are unknown.