"Triple Trouble" an Obey Me! Fanfiction (Multiple MCs AU)

          It was about a week from when the year started. Since the time Tara made pact with Mammon, the demon began to slowly get used to spending time with the three humans. Yet he noticed the humans had been participating in a strange activity. Every day after school, they would go directly to their room, and would stay there locked for hours, not letting anyone in. He hated to admit it, but it was slowly staring to annoy him. What were they doing there? Why they refused to tell anyone? It was this day, he had just enough, and was determined to find out what was actually going on.

          "Hey, Beel!" Mammon shouted at his brother as he passed him in the hallway, just when the white haired demon headed to the room humans were once again squatting at.

          "No, you can't borrow any money from me." Beelzebub said coldly, as he stopped and glanced over his shoulder at Mammon.

          "No, that's not what I want. Now, at least. Do you know what the hell are the humans doing in their room all the time?" Mammon asked, placing his hands on his hips.

          "How would I know? It's none of my business." Beel responded with only zero interest. Unlike Mammon, who was clearly bothered by it.

          "I just think it's weird, y'know? I swear I heard weird sounds coming from there the other day." Mammon truned to the side and looked at the door of the room they were talking about. Or, well, what Mammon was talking about.

          "If you want me to help you sneak in there so you can steal from there, ask someone else." Beel spoke coldly, before turning to leave again, having no interests in Mammon's suspicions.

          "Wait, that's not- damnit. Fine! I'll do it myself!" Mammon shouted at Beelzebub as he was leaving, before speedwalking to the room of the three humans. First, he leaned against the door and listened. Beside a very strange sounds he couldn't quite identify, he heard them talk. Something along the lines of, "this is going to be great", "I can't believe how fast it went" and "we're gonna get in troubles for this," which got him only more curious. He had to find a way to get in. That was when it hit him. The window.

          It was a stupid idea, that's for sure. But it was too late for Mammon to realize that, when he was hanging on a rope from the roof, and was slowly sliding down to the level on where was the needed window. Luckily for him, the curtains weren't closed, and the window was even open. Perfect. He leaned closer to see and hear better, but what happened he didn't expect. A very strange and strong scent slapped him over the nose, causing him to almost fall down. What the hell was that? He couldn't help but cough.

          "What was that?!" Muis yelped, rushing over to the window. But before panicking Mammon could find of a way to hide, Muis stood there, staring at him, having on a face mask for blocking chemicals.

          "Uh, hey. It's totally not what it looks like." Mammon chuckled awkwardly, holding for his dear life on the rope.

          "Guys, we have a bad ninja here." Muis said with a pure poker face as she turned back to the room, speaking to her two roommates.

          "Let him in. There's no point in hiding it now anyway." Tara spoke from inside the room. Muis nodded, and stepped aside, so Mammon can crawl in. And so, he did.

          "Here, take this." Muis offered Mammon the same mask she and the other two had on their faces. The scent inside was even stronger than outside, so he slapped it on immediately. Then the demon looked around, blinking. The humans turned their room into something far too similar to a chemical lab. Some barrels, some tubes, and several bottles of clear liquid.