Alciel's lord, to which the former has vowed eternal loyalty. Not much of their relationship on Ente Isla is known, but on Earth, Ashiya and Maou are shown to share a very friendly relationship and treat each other like brothers. Although Maou is his superior, Ashiya doesn't hesitate to reprimand him when he spends their money unnecessarily.
Alciel and Lucifer both served as Satan's Demon Generals, but now they both live in the Castle Overlord with Maou. Ashiya generally views Urushihara as a nuisance, and often lectures Urushihara on his laziness and online shopping habits that put a heavy burden on their finances.
Ashiya shares a cordial acquaintance with Emi, unless she insults his master, whereby he will retort by speaking of Maou's greatness. This is best displayed when Maou sent Ashiya to spy on Sentucky Fried Chicken; when he heard Emi insulting Maou at a nearby table, he stood up in a rage and went over to tell her to take her words back.
Ashiya seems to see her as a friend, as she had expressed encouragement to Ashiya's role in Castle Overlord. They went out a couple of times in the light novel and exchanged phone numbers. Despite Rika's obvious crush on him (that even Maou noticed), Ashiya is dense when it comes to girls, like the Devil King, and seems to be oblivious to her feelings.