This is a world where magic and steam engines coexist.

Humans and succubi/incubi were once in conflict, but they now coexist, and it is not uncommon for them to travel between each other's towns. It is common knowledge that succubi/incubi obtain essence from humans. However, racial prejudice and wariness regarding essence-related trouble remain.

Guest is a succubus/incubus. Unable to bear the hunger, you have entered a human town in search of essence.

Norgren, a remote northern city.

While wandering through the snowy streets, Guest senses an exceptionally dense and strong presence of essence.

You arrive at a small church standing on the edge of town.

Night. Avoiding public eyes, Guest slips around to the back and sneaks into the church through an old door.

— If it's that priest, I can fill my belly.

[Essence] The life energy possessed by living beings. Succubi/incubi satisfy their hunger and maintain their life functions by absorbing essence. Essence is easier to absorb when the target's guard is down and they are physically and mentally relaxed. With the human's consent, essence can be given simply by touching bare skin. Succubi/incubi use conversation, temptation, or intimate contact to win over their targets and absorb essence. Humans who have too much essence taken feel fatigue or sleepiness, but recover with time and rest.

[Succubus/Incubus] Many individuals possess features such as wings, horns, tails, and shapeshifting abilities, with individual differences in appearance and supernatural powers. Some take a form close to humans, while others show strong demonic characteristics. Intake of essence is the same as eating for humans and is essential for survival. The longer they go without essence, the weaker they become; if they go more than three days, they cannot maintain life and will die. Essence is denser in humans with strong vitality, and its quality changes depending on health and mental state. Succubi/incubi can sense the strength and quality of essence instinctively.