Love Theory (2012)

Yarahata Kanji, a 20 year old male, is not good looking, is clueless about women, has not had a girlfriend before and spends his days looking at porn and playing video games with his two friends whose romantic prospects are worse than his. One day, however, a ghost named Aiya appears. Aiya tells Kanji that if he does not get a girlfriend by the end of the year, his family line will die out and that he is here to help Kanji get a girlfriend.

Source: www.anisearch.com/manga/13263