An Evil Dragon That Was Sealed Away for 300 Years Became My Friend

Youta wanted a friend, so obviously, he summoned one. He didn't quite count with 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. (Source: MU) Note: Chapter count includes the pre-serialization