A boy is fond of an angel that kills him again and again.

Imagine a world where the secret to immortality has been discovered, causing women to stop aging by the time they turn twelve. Sounds like it might be a perfect playground for a discoverer with less-than-wholesome interests, doesn't it? That's exactly why the Big Man Upstairs sends Dokuro-chan, one of his angelic assassins, into the past to "deal" with the sicko who messed with nature. But Dokuro-chan decides instead to move in with her target, Sakura Kusakabe, and keep him too occupied to find eternal life.—Crunchyroll

Sakura Kusakabe, a mere junior high student, has committed a horrible crime. Or, rather, he will commit a crime-20 years into the future. The crime in question? He will prevent all women from developing past the age of 12, with immortality as an unintended side effect. As a result, the angel Dokuro Mitsukai is sent from the future as an assassin, armed with with a magical spiked bat named Excalibolg. However, rather than kill him, Dokuro wants to take a different approach. She resolves to be a constant nuisance to Sakura, in an attempt to prevent him from focusing on anything long enough to create his criminal technology. With Dokuro going against orders, the angel Sabato is sent out to complete Dokuro's mission. Between the impulsive Dokuro-who often murders Sakura with her bat before reviving him with the magic words "Pipiru piru piru pipiru pi"-and the electric baton-wielding Sabato, Sakura's life will never be peaceful again.—MAL Rewrite