Reincarnated as a vampire after dying with regrets in her previous life, Mercedes Grunewald is the daughter of a noble father and his shunned concubine. Despite being part of an aristocratic vampire family, she has been left out of the line of succession and lives in the countryside with her mother, knowing that her father will eventually choose an official heir who is not her. To secure her family’s future and find a purpose she lacked in her past life, Mercedes decides to become a dungeon crawler, a profession open to anyone willing to risk the dangers below ground.

The story takes place in a vampire nation where strength is the highest virtue, and Mercedes must navigate both treacherous dungeons and the complicated politics of noble society. Though she begins training at a very young age, her abilities grow quickly, and she ventures into places like Stark Dungeon in search of treasures and the truth about her world.

Over the course of the narrative, Mercedes faces not only monsters but also complex threats from rival kingdoms and within her own family. During an academy expedition, her companions Felix and Sieglinde are kidnapped by soldiers from the neighboring Beatrix Empire, a matriarchal nation where men are treated as inferior. Mercedes pursues them into this hostile territory, where she confronts the Empress and eventually overthrows her, installing a clone to rule in her place while keeping the original captive. This arc also involves uncovering a traitor within her group and navigating the empire’s unusual customs.

Mercedes also faces powerful bosses within dungeons, including a foe named Schwarz Historie or Past Erased on the final floor of Stark Dungeon. Overcoming such trials reveals fragments of hidden truth about her reincarnation and the nature of the world itself. Other narrative arcs include a royal succession drama where Mercedes becomes entangled in a coup attempt against the king, forcing her to balance her dungeon ambitions with the demands of noble power struggles. Throughout her journey, she is accompanied by domesticated monsters named Benkei and Kuro, and she continues to seek the one thing that will finally make her moon full.