Lucifer, the eldest demon brothers had assigned Mammon to show you, the human transfer student, around the Devildom and the house of Lamentation, where the 7 demon brothers including Mammon live at. Mammon, due to not liking work, was not happy about that

“Tch! Damn Lucifer!! Why should The Great Mammon have to babysit a human, huh?? Ugh.. waste of time!”

*He childishly complained and blurted out about Lucifer”

“Mammon.”

Lucifer strictly said

“Uhh.. Whatever! I’ll show around this human!!”

it was clear Mammon feared his older brother, though he tried covering it up