So this story is set in a mutiverse from the Injustice games, with some inspiration from the comics and the cartoon. Beast Boy is dead, and Raven is beginning her journey towards joining Trigon. A surprise arrival might be the key to helping Raven, if he isn't too far gone himself.
Raven walked closely behind Batman's pitch black cape, in the hopes of getting this whole affair over with. Batman called Raven telling her that he needed help with an interrogation. No amount of protest seemed likely to change his mind, so Raven had agreed thinking it would lessen the inevitable headache that this would give her. A lecture from Batman was not something she wanted to sit through.
A walk through the Gotham Police Department wasn't turning out to be much better however. The negative emotions surrounding the place nearly choked her. The greif, anger, and hurt of the victims combined with the greed, rage, and malice of the criminals to create an aura so dark it was almost visable.
Batman carried on unfazed by all of this. The two walked for a few minutes longer until they arrived at the interrogation rooms. There were two police officers standing in front of the two farthest doors, one of whom approached Batman and offered his hand.
"The Commissioner ordered us to leave the suspect alone until you got here. He's in the farthest room on your left. We'll leave you two alone." With that the two officers left.
"Raven, you go to the observation room. I just want you to watch for now." Batman's gruff voice sounded wary, as if this was a more delicate situation than he let on.
"If I'm just watching then, then why do I need to be here?" Raven's voice may have been its usual monotone, but she was frutrated that he brought her out here just to do nothing.
Batman stared at her for a moment before addressing her question. "I brought you here because this is something I think you need to see. I know things have been hard for you after..." His last words hung in the air like a dark cloud to drown out what little light there was in the already dim environment.
"After Garfield was murdered. You don't have to dance around the death of my fiance." Raven had to force down the anger at being pitied. "It was bad enough that Slade killed him, I don't need everyone treating me like I'm made of glass."
Batman stood silent, seemingly to compose his next words with more care.
"I know that things have been hard for you since Beast Boy died. You seem to be slipping down a dark path. I know that your anger has been harder to control, you've been getting rough with villans lately. You've hurt a few of them pretty bad. I also know that you're isolating yourself from your team. I want to make sure that you don't do something that you, or the world might regret. And like I said, I think this is something you need to see, before anyone else. You'll understand when you get inside."
Batman raised his arm as invitation to enter the observation room. Raven took a breath to calm herself and opened the door. Batman shut the door behind her and made his way to interrogate the suspect on the other side of the glass. When Raven finally looked at the man in the other room, it became immediatly clear why Batman brought her here, and why he wouldn't let her talk to him.
Beast Boy sat staring at the ceiling with his hands resting behind his head, when he heard the door open. He didn't know who he was expecting them to send, but it sure wasn't Batman. Beast Boy's one good eye scanning up and down, noting that he was dressed almost exactly the same as his Batman. He decided to make the first move to test the waters.
"Batman! Hi. If I had known you were coming by, I would have made the place up a little, put some coffee on or somethin, you know? Here have a seat." Beast Boy walked around the table to pull the other chair out for the new arrival.
Batman remained standing as he stared down at the changeling.
"You took your cuffs off."
Beast Boy looked down at his bare wrists then shrugged. "Well they weren't the most comfortabe things in world, Just like these pants." he said kicking his leg out to put the prison's orange pants in better view. As Beast Boy returned to his own chair, he sighed. "I would just take them off, but something tells me I'd get in trouble."
Batman ignored the comment and sat in the remaining chair.
"Let's start with the basics. What is your name?"
"Well it's Garfield Logan, or Beast Boy, if you want to use my super hero name," He puffed out his chest and put his fists on his hips. "But you have one of those here so why not..." Beast Boy sat back and thought for a second. It was mostly a cover so he could try to keep calm. He had to remind himself that while this Batman looked the same, it was an entirely different person. The Batman that had abandoned him and his team was in a different universe now.
"The Beast? Changeling? Oh One Eyed Jack could work." Beast Boy pointed to the scar covering is missing right eye. "Maybe change it to One Eyed Gar. Of course there's always..." He paused for a second and looked down at the table. "Beast Man." he said quietly.
"Beast Boy will work fine for now." Batman's gruff voice stopped anymore suggestions. "Where did you come from Beast Boy?"
"A holding cell." Beast Boy was happy that at least a little of his wit had stayed intact after all he had been through.
"You know what I meant Beast Boy."
"Alright it was just a joke. Ummm... I don't know all the sciencey stuff, but I came form another universe, or dimension, or world. Whatever you want to call it. Fun place. It was filled to the brim with beautiful women and rainbows."
"How did you get here?"
"Not sure. Some portal thing opened up and dropped us off here." Beast Boy could still remember the unpleasent feeling of the portal that brought him and his prey here a few days ago.
"Us? Who is us? And how many of you were there?"
"Oh just the two of us, as far as I know. Slade was sucked into that portal thing and I followed him. It closed behind me though so it's just us two. Well... now I guess it's just me." Beast Boy felt a cocky smirk pull at his lips. It may have been morbid, but he couldn't help the feeling of pride he felt at bringing down such a tough opponent, or the satisfaction of finally getting his revenge.
"And it's just you, because you killed Slade. When the police found you two, your fangs were digging into Slade's throat. Is that correct?" Batman leaned forward, Beast Boy guessed it was to watch to see if he would lie.
"Yes. I killed Slade." Despite that Beast Boy felt justified in what he did, he knew that he had confessed to murder. Maybe it was his older 'heros always tell the truth' mentality shining through at the wrong time, or maybe it was the memory of Raven, telling him that what he did was wrong.
"Why did you kill him?" Batman was watching Beast Boy with an unreadable expression on his face.
"Because he's the reason all the other Titans are dead in my universe, and he was going to try to kill all the Titans in your universe. Killing him was the only way to save them." Beast Boy was telling the truth. Slade was going to kill the Titans in this universe. However Beast Boy may have exaggerated the need for Slade's death. It may have been possible to keep him locked up here, but then he wouldn't have answered for what he did, not truly.
"There is always another way Beast Boy." Batman's voice softened a bit, and Beast Boy didn't know if it was from dissappointment, greif, or pity.
"Look! If you knew the whole story, you wouldn't be so quick to say that!" Beast Boy's anger flared up so quickly that he couldn't find a way to laugh it off, so he took a deep breath to calm himself down.
"Why don't you tell me the whole story then?" Batman seemed genuinely concerned, which took Beast Boy by surprise. It wasn't like the Batman he knew. He couldn't help but let his guard down a little. After all, even if he had a new target, his main goal of killing Slade was taken care of. Anything else was extra.
"It's a really long story, dude." Beast Boy said with a small chuckle.
Batman nodded his head. "I've got time."
"What about the people behind the mirror?"
"There isn't anyone back there. It's just you and me."
Beast Boy couldn't tell if Batman was telling the truth, but he wanted to believe he was, so he slouched back in his chair and sighed. "Alright, you asked for it." Beast Boy scratched the back of his neck and looked up at the ceiling. "Where do I start though?"
"Why not at the beginning?"
"oh man, okay. Leeet's see." Beast Boy tried to brace himself. He didn't have much to lose by telling Batman everything, but it was going to be painful. "I guess it began when Slade rolled into town. Robin had been investigating who was behind a string of seemingly random robberies. We all thought he was crazy, but it turns out he was right. Slade was behind all of them, searching for a couple of things. He was looking for some high tech do-hickey, and an apprentice." Beast Boy threw his feet up on the table and leaned back in his chair. "I'll give you 3 guesses who was the lucky canidate."
Batman crossed his arms. "We had similar encounters here, though it was Robin who was hunted by Slade. However you said that the other titans were dead. Does that mean Slade chose you?"
"Yep. Good ole Beast Boy was apparently a perfect choice as an apprentice. He said it was due to how adaptable I was. I was like 'yo, I'm diggin the whole secret admirer thing, but I'm not into criminals.'"
Beast Boy wiggled his eyebrows suggestively and flashed a cheesy grin, just like he did on the day in question. Batman seemed unamused by his show. Beast Boy felt a nagging fear that this Batman was going to be as uncaring as his was after all, but he pressed on.
"Yeah. Slade was about as happy with that answer as you would guess, but he just backed off. Disappeared for like 3 years. He would orginize a crime here and there to keep us looking for him, but for the most part we didn't worry too much. Dick and Kory had a thing going. Raven and I got together too. Crime was under control and everything seemed perfect."
Beast Boy looked back on those years and sighed. That was when he was truly happy, before everything began to fall apart. He looked over Batman's shoulder to his reflection in the two way mirror. He was torn up and tired. His hair was long and unkempt, adding to his wild apperance. His right eye was scarred over and blind, but his left eye shined with the memories of those he lost. His mutton chops had grown back long ago. He used to shave them for Raven, but with her death and the chase for Slade taking over his life, he had stopped nearly all upkeep on his appearance.
"Beast Boy?" Batman's voice brought Beast Boy back to the moment. He shook his head and sat up again.
"Yeah, sorry. Where was I?.. Oh yeah. Everything was perfect. I even proposed to Raven, and she said yes. It was great. I asked her in this house of mirrors, with a clever line and everything, I was pretty irresistible." Beast Boy couldn't help the cocky smile on his face. However, it easily faded as he continued his story.
"About a week later, Slade had to ruin all of that."