I wonder what he wants, Eren wondered. Their footsteps echoed on the linoleum floors as they all awkwardly followed Erwin to wherever he was taking them.

They were all surprised when they found themselves in front of a door, reading "Authorized Personnel Only" in all caps.

"Uh, sir? Why are we here?" Mikasa asked.

Erwin didn't respond at first, placed his hand on the scanner for authentication. Then he typed in a couple things on the keypad and gestured for the others to place their hands on the scanner.

"I'll explain everything in a moment."

Jean shrugged and went to the scanner. Once they all had been scanned, the doors slid open.

"Wait," Erwin stopped Eren. "Armin can't go in."

"Why not?" Eren asked. "Whatever this is, Armin will help us a lot."

"Yes, but I'd prefer if he wasn't there unless absolutely necessary."

Eren sighed. "Fine." He turned to Armin. "Sorry, dude. You're going to have to wait out here."

"Alright," Armin responded, stepping to the side of the door.

It wasn't nearly as exciting as Eren thought it would be. No secret passageways or anything, just another hallway leading to another door.

"I'm sure you've already guessed what you're here to see," Erwin said, as he opened the door.

She looked the same as the day they found her, except now the crystal she was encased in was held up by metal supports. Connie muttered a vague Captain America reference, but Jean elbowed him.

There were also wires attached to the crystal, reading Annie's vital signs. Eren watched the steady beat of Annie's heart and wondered if she was conscious in there.

"None of our scientists have been able to get her out," Erwin began. "They can't even figure out what material the crystal is composed of. It's an extremely alien substance, and its structure seems to shift every time we try to look at it."

"Whoa...cool," Sasha breathed, walking around the exterior of the crystal. "Um...could I…?"

Erwin nodded. "I brought you here because I believe you can help. You took down the Colossal Titan, and now I want you to try and wake up his sister."

They looked at each other, not sure what they thought of Erwin's request.

Connie shrugged. "Better than going to class, in my opinion."

Erwin nodded. "Thank you. I really appreciate your service. I'll leave you to your work then."

The doors closed and Eren sighed. Connie was right, this was better than going to class, but at the same time, if none of the Institute's scientists could figure it out...how would they?

"Well," Mikasa straightened her scarf. "Let's get to work."

-x-x-x-x-x-

They worked for days. They went in early to conduct a couple tests, spent the afternoon in a couple classes, and pondered the mystery at night. Hanji provided them with pastries and coffee, and sometimes Eren would walk in at 7 am to find Sasha already staring at the crystalline structure. Turns out she had been there for hours.

Even so...Annie Leonhardt kept her secrets.

"It just doesn't make any sense!" Sasha threw her hands up in the air, pacing around the room madly. "I've test every element there is, but none of them form this way."

"Well, it is an alien substance," Connie pointed out, chewing on a donut.

"I know! So basically, we're trying to discover a new element."

"It's harder than anything I've ever seen," Jean said. He had brought in his gear one day to see if they could cut Annie out, or at least a sample so Sasha could test it more easily. "I couldn't even make a scratch."

"No magnetic properties either," Mikasa added.

"Extremely resistant to heat." Connie pitched in. "The thing stayed like an iceberg when I heated it up."

"You tried to heat it up?!" Jean screeched. "You realize that could have been dangerous for her, right?"

Connie waved his donut in the air nonchalantly. "Relax. Her vital signs never changed."

Eren groaned. "I don't know how to solve this either, guys."

"Do you think Armin could help?" Mikasa wondered.

"Armin only knows things that he's programmed to know," Eren sighed. "We don't know what it is, so Armin definitely can't."

"No, I agree with Mikasa," Jean cut in. "There must be something we're missing. Maybe Armin could scan the crystal and maybe detect something we can't."

"Professor Erwin's been pretty tough about not letting Armin in here though," Eren reminded.

"Talk to him about it," Sasha said. "I'm sure he'll understand if we explain the situation to him."

Eren shrugged. "It's worth a try, I guess."

They picked up Armin from outside and made their way down the hallway to Professor Erwin's office.

"Professor Erwin?"

Erwin looked up as the six walked into the room. "Oh, hello. What can I do for you?"

They had decided that Mikasa should be the designated speech-maker. "We haven't been able to make much progress with Annie. We've tested the crystal and even tried to cut her out forcibly but nothing works. We were wondering if we could have your permission to bring Armin in. We think that he could scan the crystal, maybe pick up on something that we missed."

"I would prefer if you didn't," Erwin said.

Mikasa hesitated. "I thought you wanted us to get Annie out of the crystal. We're trying everything we can think of."

"Armin will retain the memory of being in the chamber. This is a top secret assignment, and if word gets out that we're facilitating a person in the Institute, it won't end well," Erwin explained.

Eren opened his mouth to say something but Erwin stopped him. "It's not up for discussion."

They were forced to leave. As soon as the door closed behind them, Eren groaned.

"It just doesn't make sense!" he complained. "Professor Erwin's logic doesn't even make sense. I can delete the memory from Armin's chip, it's an easy push of the button."

"Maybe he doesn't want to take the chance that something could happen," Jean suggested.

"Yeah," Eren sighed. "But he trusts us enough to ask us to help with this...wouldn't he trust us with this one little thing."

"You're right, Eren," Mikasa's eyes were narrowed in thought. "There's something weird going on here."

"Then what do we do?"