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Keima Katsuragi, a second-year high school student, is an avid Bishōjo game player. He is known on the Internet as "The Capturing God" for his legendary skills to be able to "capture" any 2D girl in games. However, in his actual school life, Keima is known as otamegane (オタメガネ), a derogatory portmanteau of the two words otaku (オタク) and megane (メガネ-"glasses") and is considered nothing but a gloomy geek with thick glasses.
At the start of the series, Keima receives an e-mail offering him a contract to "capture" girls. When he accepts it, thinking it is an invitation to a game, a demon from Hell named Elsee appears. She asks for his cooperation to help her in catching runaway spirits. These spirits hide themselves inside the hearts of girls', and Elsee suggests that the only method to force the spirits out is by "capturing" the girls hearts—making them fall in love with him and filling up the gaps which the runaway spirits hide in. Interested only in 2D girls, however, Keima is appalled by the idea and refuses the assignment as he has no romantic real life experiences whatsoever. Nevertheless, with the contract already executed, Keima has no choice but to help Elsee no matter what; if they fail, it is Elsee and Keima who will lose their heads.