The Devil Is a Part-Timer!, Vol. 16 (light novel)

This is the story of when the Maou the MgRonald employee was still Maou the Demon Lord! Right as Alciel brings more allies into the fold of the newly formed Demon Lord army, Lucifer rises up in revolt! Fed up with the way he's been treated, the the upstart rebel obliterates Maou's fortress and flies off, starting a wild goose chase that leads Maou and his comrades to the treacherous south!