Sakura Kusakabe is an ordinary junior high school student, but he harbors a dark secret—one that he will hold twenty years in the future. His future action: preventing women from aging past the age of twelve, thereby granting them immortality. To stop this, the angel Dokuro Mitsukai is sent from the future as an assassin, wielding a magical spiked club called Excalibolg. However, instead of killing Sakura, Dokuro chooses a different method, deciding to constantly harass him in hopes of disrupting his focus and preventing him from developing the forbidden technology.
Going against her mission, Dokuro's actions lead to the dispatch of another angel, Sabato, who is assigned to carry out Sakura's assassination. Caught between Dokuro, who frequently knocks Sakura unconscious with her club before reviving him with the chant "Pipiru piru piru pipiru pi," and Sabato, who wields an electrified baton, Sakura's once-normal life becomes anything but peaceful.