Currenlty, there is only a manga available for this. It's done by Nobuyuki Anzai, creator of Rocket Princess and Flame of Recca. You can find scanlations here
Ginta is you basic average...nerd, with a BIG imagination. One day, he has the same dream for the 102nd time and suddenly, at school, his class is transformed into a portal. He enters it leaving his world, his mother, and Koyuki, his love, behind. He ends up in the magical world of Mär Heaven where magical beings exist and people posess magical items called ÄRMs. These items have a number of different abilities and appearances. Now he must learn to control their power and find a specific one, Dimension ÄRM, if he ever wishes to return to his old life
