Zantei Kanojo: Binkan Fighter

Murakami Yashiro lives a pretty isolated life and is more interested in virtual girls than in the real thing. One day, his grandfather changes his life forever by throwing him into an all-girls school that he happens to run. His grandfather is determined to have Yashiro get himself a real girl, and therefore not bring shame on their family's name. To that end, he makes a school rule that seducing Yashiro is a requirement for anyone to take the coveted position of student council president. To gauge the success of female candidates, his grandfather puts an erotic meter on Yashiro's forehead, which hits 100% at a successful seduction.

Many girls are eager to use Yashiro to acquire the position of student council president, and the current president, Masamune Momiji, will have her hands full trying to keep Yashiro's attention and her rank. Yashiro has a huge crush on Momiji, but would she ever see him as anything other than a means to preserving her position?

(Source: MangaHelpers)