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

Youta wanted a friend, so obviously, he magically 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.

A serialization now exists, though the chapter numbering is not straightforward.