An Evil Dragon That Was Sealed Away for 300 Years Became My Friend (Pre-serialization)

outa wanted a friend, so obviously, he magically summoned one. He didn't quite count on the fact that he'd summon Mumu, a mighty and evil dragon girl, notwithstanding that, due to hundreds of years of imprisonment, she's very needy, very weepy, very clingy, and lonelier than the button "9" on a microwave oven. A promotional pre-serialization series.