The World God Only Knows

Keima Katsuragi is famous on the Internet as "The God of Conquest": there is no Dating Sim that he cannot beat, no heroine whose heart he cannot conquer. However, in Real Life he's an introverted and unpopular Otaku Jerkass who hates all real girls.
One day, he receives a provocative email asking for help in conquering some hearts. He rises to the challenge, inadvertently making a Deal with the Devil to help Elsie, a low-ranking devil from Hell, re-capture some runaway spirits. These spirits hide in the hearts of troubled girls, and the easiest way to force them out is to have the girl fall in love. And if Keima fails, then it's Off with His Head!
Thus begins Keima's daunting task, which throws him deep into exactly what he's been dismissing: Real Life, and more importantly, real girls.