Disclaimer - I don't own The Devil is a Part Timer!/Hataraku Maou-sama! or any characters involved. Copyright to Satoshi Wagahara, White Fox and Funimation.
Headcanon: Urushihara sometimes gathers magic from minor disturbances while he's home alone (behind Maou and Ashiya's back)
In Case of Emergency
He hadn't had so much time to himself in ages.
Lucifer, now renamed Hanzo Urushihara, was alone in the new Devil's Castle. Normally, this wouldn't last too long. Although Maou did take on more than a few shifts at work, Ashiya was never gone for anything over an hour or so. Shopping, usually, or on the occasional mission given to him by his king. But this time, on top of his regular chores, Ashiya was apparently meeting up with someone. Urushihara only knew that this someone was a co-worker of Emi's, he didn't really care enough to question him any further.
The first couple of hours was spent like any other time he was alone; try to research magic, get distracted by something else, end up scrolling through page after page of the most random websites, devour whatever junk food was in the kitchen and order a new game in time for same-day delivery. But there didn't seem to be much else to do.
Even he could get bored of just sitting at a computer for an extended period of time, especially when he wasn't used to this free time or privacy. Not wanting his legs to fail him and fall asleep again, he stood to stretch. Wasn't there something better to do…?
He didn't get to finish that thought before the ground started shaking. It wasn't a particularly bad earthquake, but it was enough to make Urushihara stumble slightly. He regained his balance only to hear a child's cry outside. Curious, he opened the window and leaned out. Across the street he could see a slightly panicked mother fussing over her crying baby as she hurried to steady its stroller which, he guessed, had somehow fall over in the earthquake.
Urushihara didn't really see any point of interest in this and began to turn away. That is, until he sensed something. Both humans were releasing negative energy. Not much, but it was there. And it was finding its way right to him.
How long had it been?
Now, Urushihara didn't have much need for magic in his current state. He was comfortable enough where he was, and in all honesty it was really only Maou who had a good reason to be feeding off of human negativity like that.
But then again, it could come in handy someday to have a little extra magic stashed away.
Ready.
Just in case of emergency.
They don't need to know, right?