High schooler Mizushima receives a Valentine’s Day gift of chocolates from Monami, the new student. Unbeknownst to him, the chocolates are infused with Monami’s vampire blood. After consuming them, he becomes infected, and Monami reveals her desire to spend eternity with him as vampires. Mizushima decides he wants to fully transform into a vampire with Monami’s assistance. However, his girlfriend Keiko witnesses them kissing on the school rooftop and, in a fit of rage, tries to push Monami off but ends up falling herself. Keiko dies, but her father, the eccentric scientist Kenji Furano, brings her back to life as Franken Girl. This sets the stage for a fierce battle between Franken Keiko and Vampire Monami, all in the name of love.