The protagonist is reborn as a vampire. However, the family she is born into is noble, but her mother is just one of the concubines, and her treatment is far from favorable. She and her mother are isolated in a dilapidated house, and it is clear that they will be abandoned someday. She can barely survive now because she has inheritance rights, but eventually, the family will be inherited by the legitimate child. While that may not matter much, she must prepare to survive on her own if she is ever abandoned. Fortunately, this world has dungeons, and there is a job called a Seeker who explores them. So, her goal is to conquer the dungeons. She will dive into the dungeons, earn money, become stronger, gather companions, and dive again. Thinking about her previous life, which was lived without purpose and ended in a boring death, Mercedes Grünwald strongly desires, 'Because it's my second life, I want to live without regrets and die with a smile. This is the story of how the waning moon becomes full, and she ends her life with a smile.'