For those who wonder, it is the story of of an angel, Dokuro-chan, who is sent in the past to prevent Sakura Kusakabe, our protagonist, to build a age-stopping machine that will make all the girls stop age at preteen-state and turn the future into a pedophile-world. Her primary goal is to kill the guy, but she falls in love with him, so instead of ending his life, she preserves it using her angel powers. But due to her temper, she keeps killing him, but using her powers to bring him back together and apologize.
It's one of my favorite animes, made me cry at end
http://www.animenewsnetwork.com/encyclopedia/anime.php?id=5094
--by Miko Miko, for KonataChan, of animesuke. *borrows without permission, but with credits* ~_^
