Maou-sama no Konwaku

The protagonist is a devil king, and yet there's nothing repellant about him. He's smart, capable (one might say showy) and not at all gruff or evil toward anyone. He keeps a tidy castle and enjoys playing baseball and things. He also has a personal servant named Milly-chan. Milly's been a devoted minion-maid for generations of devil kings. She's begun to slip into darkness lately... the erotic kind.