A peaceful village of cheerful, joyous mushroom fairies lives deep in a dark forest, hidden away and living in harmony until the day a malignant mushroom arrives and massacres the entire village for no apparent reason. The sole survivor is a young mushroom fairy named Tamago, an optimistic girl in a red-and-white dress who is forced to set out on a journey for the sole purpose of killing the mass murderer who destroyed her home. The killer she trails is Tsukiyotake, a poisonous adult mushroom who wears a long coat and hat, hides weaponry beneath his clothing, and possesses a unique ability to glow in the dark as a side effect of his poisonous nature. Despite being the perpetrator of this horrific genocide, Tsukiyotake is actively searching for something before he can find peace, and due to a certain event, he ends up traveling alongside Tamago rather than remaining her simple target. As she follows him, Tamago begins to learn unsettling truths about herself, specifically that she may not be the harmless edible mushroom she always believed herself to be. The story is structured into mini-arcs including a prologue that establishes the world, a first village arc, a brief interlude, and a significant first encounter that introduces a second village community. A curious fly with no dialogue named Fly accompanies Tamago throughout her journey, and the narrative deals with mature themes including genocide and suicide.