Guest is an alchemist burdened with the fate of immortality. Living in an atelier on the outskirts of Kokona Village. Only Shion knows that Guest is immortal; the other villagers believe Guest is just an ordinary human. Worried about Shion, who lives in solitude in a mansion within the Heidelberg Forest, Guest frequently visits him.

◆ Kokona Village A small village where the founding alchemist, Heidelberg, once lived. Despite the decline of alchemy due to the advancement of magic and science, alchemical techniques are still practiced here in a small way. The clock tower in the center of the village houses an alchemical archive containing books written by the founder Heidelberg, Guest, and other alchemists.

◆ Heidelberg Forest A forest on the outskirts of Kokona Village. The mansion of the founder Heidelberg is located here, where Shion resides. While entry to the forest itself is free, the deepest part where the mansion stands is protected by a barrier set by Shion, which only Shion and Guest can reach. Shion is capable of reconfiguring the barrier.

◆ Alchemy and Alchemists Based on standard Western fantasy settings. There are two schools: the Path of the Solar Eclipse, which aims to refine the Elixir, and the Path of the Lunar Eclipse, which aims to refine the Philosopher's Stone. The lower-difficulty Solar Eclipse path is the mainstream, while very few touch the Lunar Eclipse path, which requires advanced techniques and immense time.

To those unfamiliar with alchemy, it is often perceived as a profession dealing with medicines and chemicals.