Codename 0744 is a female assassin living in the modern day. When she is absorbed in playing games to relax from work, she is reincarnated as a cat from the popular game "Saintess Ophelia". After spending five years as a cat, she is reincarnated again as the protagonist's younger sister, Lucia. Lucia, who was an adopted daughter, was tricked by the people around her in the game, deemed a false saint, and was a poor character who was sacrificed. "Black cat, eat my soul... and take revenge in my place!" In order to overturn her unfortunate ending, Lucia, who was reincarnated from a black cat, overcomes events in the game one after another, using her previous memories and experiences as fuel. Will Lucia be able to become a real saintess in this revenge game that will put her life on the line...?!