Remus woke up to shoutings. He shared his dorm with two Gryffindor boys— both younger than Remus, and Remus didn't even bother learning their names. "You lost my sweatshirt!" One was shouting, whilst the other was looking everywhere to find the sweatshirt.
"Hey, can you guys be quiet?" Remus said silently. "I'm trying to sleep."
The curly-haired, shorter boy didn't even look at Remus. "I don't care," he said. "Go sleep somewhere else."
Remus didn't feel angry. He stood up, wore a hoodie and walked out the dorm. He looked at the time— it was two a.m. and he was supposed to be sleeping. It had been two days since the full moon ended and Remus felt more tired than ever. He thought of sleeping in the Common Room, but that'd be lame, he said to himself, so he walked out the Common Room too.
Wandering around the empty castle quietly, even though Filch saw him, he didn't say anything to the boy, since all staff at Hogwarts knew about Remus' condition. When he saw a door he had never seen before, all of a sudden, he knew he had to enter it. This urge inside him— it told him to open the door.
He got a little closer to the door and held the knob. You're not young anymore, he thought. Just get in.
So he did. He opened the door and found a master bedroom inside. There was a big bed, clean clothes, a shower and— The Mirror of Erised. Remus looked at the big mirror and didn't want to look in it. He didn't want anything from this life and he knew this mirror would show him his greatest desires— but he didn't have any. So instead, he went to the big bed and got inside. For a few seconds, he questioned if this could be a trap— something a Death Eater would do. But no, Remus knew this wasn't related to the Death Eaters. He knew this magical room. It was the Room of Requirements. He needed a bed, a nice room, so the Room of Requirements gave those to him. Feeling grateful, he lay down to sleep. Just about to close his eyes, he heard the door knob move. He could feel his heart in his chest, his fingers shaking and feet freezing. He turned to look at where the door was— to see who came. "What the heck—" the person who opened the door said. When his silhouette turned into a real figure, Remus saw Sirius Black. He was wearing Gryffindor pyjamas, his long hair made into a messy bun and eyes as tired as Remus. When he saw Remus, too, he looked surprised. "What are you doing here?"
Remus didn't give any hints. "I should ask you the same question."
Sirius shrugged. "I've never seen this door before," he said. "Is this your room or something?"
The boy shook his head. "No," he got out of the bed. "This is the Room of Requirement. It appears when a wizard is in desperate need of it."
"Cool," Sirius smirked. He checked his whole body out. Then looked back at Remus. "Nice pyjamas."
Remus didn't look at him. "Thanks," he replied, then watched the boy walk to the Mirror of Erised. Sirius looked in the mirror as Remus was watching him from behind. His expressions were unreadable, but he didn't seem happy. "What do you see?" Remus couldn't hold but ask the boy. Sirius didn't respond for a few seconds, then, just like he didn't hear what Remus said, "What is this?" he asked. His voice was shaking.
Remus walked next to the boy and tried so hard not to look into the mirror. "What do you see?"
Sirius didn't look at Remus. He was still focused on the mirror. "My brother," he said. "and me. Together."
Remus looked at Sirius. He didn't know about The Mirror of Erised and his greatest desire was— to be with his brother? Remus wondered what it was with the Blacks. "It's the Mirror of Erised. It shows you your greatest desire."
Sirius didn't flinch. "My greatest desire… Is to be with my brother?"
"Now? Yes," Remus said. "In a few years? Maybe it'll change."
Sirius tried hard to not make eye contact with Remus. He didn't say anything, and it was the first time Remus saw him with such seriousness. Sirius was always a funny, full of joy kind of a guy and even though he had his ways and elegance to himself, he was always happy. Right now— he looked too sad. "Whatever," he said, walking back to the door. "I should leave you to it. Good nights."
Remus tried to hold Sirius' arm and ask if he wanted to talk, but it'd be absurd. So he didn't say anything. Sirius left, and Remus lay back to his bed. Just about to shut his eyes to fall asleep finally, he couldn't help but stand up and walk right in front of the mirror.
He looked at it and saw nothing. There was nothing. No sign of Remus, no sign of The Werewolf. Remus only saw emptiness.