Open! The Door to Another World!!.Ginta Toramizu, an otaku-ish high school student, has had his 102nd dream of a fantasy world that goes by the name of MÄR-Heaven, and is subsequently subjected to many jeers from his classmates because of that, save for his childhood friend Koyuki. One day when he is briefing her on his newest dream, a phantom clown appears and claims him as the chosen Earth dweller to be permitted entrance into that very same wonderland. His embarkment into MÄR-Heaven is greeted by the meeting with a mysterious, beautiful witch named Dorothy and primary knowledge of the powerful magical artifacts existing worldwide – the ÄRMs.