Thirteen-year-old Kusakabe Sakura is destined, twenty years in the future, to develop a technology that freezes women's physical aging at age twelve. An unintended side effect is human immortality — which offends God. Assassin angel Mitsukai Dokuro is dispatched from the future to eliminate him, but decides instead to prevent the invention by keeping Sakura constantly distracted. Her method involves frequently killing him with a massive spiked club called Excalibolg, then immediately resurrecting him with a personal chant. A second assassin, Mihashigo Sabato, is eventually sent to complete the original mission.