悪友の俺がポンコツ騎士を見てられないんだが、どう世話を焼きゃいい? ～まどめ外伝～•Akuyuu no Ore ga Ponkotsu Kishi wo Miterarenai nda ga, Dou Sewa wo Yakya Ii?: Madome Gaiden

An Archdemon's (Friend's) Dilemma: How to Babysit a Crybaby Knight

Archdemon Zagan hires his unsavory friend, the sorcerer known as Purgatory Barbatos, to guard Archangel Chastille Lillqvist from the shadows. Barbatos takes to watching over the girl—which really means watching her constantly screw things up, trust people she shouldn’t, and inevitably bawl her eyes out. But something about Chastille and her waterworks may just have a special effect on the sourpuss sorcerer... The tale of this odd couple begins after the seventh volume of Maou no Ore ga Dorei Elf wo Yome ni Shitanda ga, Dou Medereba Ii? (Source: J-Novel Club)