Realize Me (2002)

Main character is a nerd who attends a vocational school, but aims at becoming a scenario writer. He wants a girlfriend, but is afraid to confess his feelings, so he becomes obsessed with game girls instead. One day he starts to play a trial version of a new game and manages to call the heroine to his room. She seems to have an ability to open the gate between the fictional and real world. She looks very friendly, but she's a heroine from a 18+ game, right?