The provided chapters introduce the protagonist, Lean Bloodlord, a 17-year-old vampire princess and "Revenge King." Formerly a bullied high school student named Senjou Yona, she was reincarnated as a vampire by the goddess Isuzu after her vampire village was destroyed by humans, leading to the loss of her family and friends. Fueled by a desire for revenge, Lean joined the Demon Lord's army, quickly rising through its ranks due to her talent and effort. She eventually became the second-ranked "Ghost God General" among the elite "Four Demon God Generals." Lean is gentle towards demons but fiercely aggressive towards humans, and harbors romantic feelings for Yomi, a former hero and her comrade.
Yomi, also 17, is a human "Sword King" with immense talent, ranked first among all beings. She was raised as a biological weapon by the Mercurius Holy Kingdom after her heroic potential was discovered. After enduring severe abuse and mental breakdown, she was defeated by Lean, saved by the Demon Lord, and joined the Demon Lord's army to exact revenge on humanity. She is oblivious to Lean's affections.
The Demon Lord's army is led by Philis Darklord, a true ancestor vampire and the Demon Lord herself, who is incredibly powerful but limited to a five-kilometer radius around her castle. She is also Lean's grandmother. Other notable members of the Demon Lord's army include Gray Christ, the "Warrior God General"; Sakura Forester, the "Sage God General" and a master magician; Viner, the "Murder God General" and a genius strategist; Tiana Forester, Sakura's aunt and the "Forest God General"; Loose Dragray, the "Flame God General"; Aron Beastlord, the "Wolf God General"; and Feria, the "Ruined God General."
The human forces are represented by Xenon, a reincarnated individual and a "Hero," and the "Holy Twelve Apostles," a group of powerful individuals including the "Divine Child" Revels Humanlord and the seer Helena. The chapters also reveal the tragic past of Lean's parents, Razer Bloodlord and Minea Bloodlord, who were killed by humans.
The narrative then shifts to Lean's past life as Yona, detailing her miserable existence as a bullied student who died in a gas explosion. The goddess Isuzu explains that Yona was meant to be reincarnated into a world with "Hero potential" but was instead caught in a fate-altering accident. Due to her strong "evil" attribute, she couldn't reincarnate as a human and was offered a chance to be reborn as a vampire in Isuzu's world, a world where demons are more civilized than humans who are manipulated by the arrogant goddess Mizeri.
Lean is reborn as Lean Bloodlord, the daughter of Razer and Minea, and experiences a happy childhood in the vampire village. She receives her status at age five, revealing exceptionally high stats that surprise her parents. Her father, Razer, is the Vampire King and a powerful fighter. Lean's peaceful life is shattered when the human "Holy Twelve Apostles," led by Edis, attack the vampire village. Razer sacrifices himself to allow Lean and Minea to escape. Minea is later killed by Noin, another Holy Twelve Apostle, while trying to protect Lean. Lean, witnessing the destruction and loss, vows revenge on humanity. She is eventually found by Yomi, who has also suffered greatly at the hands of humans, and they join forces.