The knight Fiene, who has been turned into a werewolf, and the optimistic Iris, who wears a red hood, are tracing back to "a certain potion" that has changed their relationship. One day, they feel a strange sense of discomfort from sisters they meet at a tavern, and decide to infiltrate the shop at night. To unleash powers that are not human... and above all, to continue to remain in a human body... Fiene drinks Iris's living blood and prepares to charge in, but――.