Nightmare lead them all to a special room set up just for this "training." It wasn't large, there weren't any special designs, just cots lining the walls. Twenty-one in total, one for each of them. 

The students spread out to lay down, at the Pro Hero's request. 

Izuku found himself laying between Todoroki and Uraraka, both looking nervous. Todoroki kept a blank face, but Izuku knew the tells; his thumb was picking at his other fingers' nails, the tension in his jawline, and the flicker of his tongue darting out to wet his lips. Uraraka was more open with her shaking hands and slight frown. 

Midoriya though . . . his green eyes were wary, teeth chewing on the inside of his cheek. 

One-by-one, Nightmare put them all to sleep. 

When it was Midoriya's turn, he took a deep breath before making eye contact. The woman's eyes were pitch black, nothing but shinny coal. He felt his body slump back against the pillows behind him, his mind going foggy before black took over completely. 

A jolt went through his body, and he sat back up in a rush, head spinning from the fast movements. 

Around him everyone seemed in a similar state, Todoroki coming to almost directly after him. 

"Okay," Aizawa cleared his throat. "is everyone here?" With a glance around and a quick roll-call the teacher nodded before sighing. "Alright then, let's get going." 

That's when they all took in their surroundings, it looked exactly like where they had fallen asleep.

No different. 

But . . .

Wasn't he against the other wall when he laid down?

The others were quick to realize this too, everything was the same, yet the exact opposite. 

A hall way that led to the right, now led to the left. If a door used to face the North, it now faced the South. 

Strange. 

"Now, your Other Selves woke up with you, they are now all searching for each other and for you. What they do when confronted will be varied. Each personality will vary. Everything will be varied. Do you understand?" Aizawa asked briskly, his pace a tad faster than normal. 

Cries of "Yes, Sensei!" rung out in the halls. 

"Good." 

Their teacher led them out of the building, huddling together outside the main entrance to the flip-flopped UA. 

"We don't need to look for them, they will do all the finding. What we do need to do is keep moving. That way we don't run the risk of meeting many at a time. It's best to focus on one Other Self at a time." Their teacher sighed again, rubbing the bridge of his nose. 

Tsuyu raised her hand, eyes large and filled with curiosity. 

"Yes?" Aizawa didn't even look at her, he just kept his eyes closed. 

"You sound very familiar with this. Have you gone through it before?" The frog-girl asked, a finger on her chin as she tilted her head. Blunt as always.

"Yes, I have. I was in her class at UA. We sparred a lot. There were a few times she didn't pull me out in time because we were doing group fighting." His shoulders slumped. "So, yes, I do know what my Other Self is like. And that's why I was against this whole thing in the first place." 

"Is your Other Self dangerous?" Kaminari asked, becoming slightly worried. 

"Yes." He sighed, yet again, before motioning for them to keep walking with him. "You can be hurt in this world, but you will heal much faster, and you don't really need food or water. Your quirks work in here, but so do you Other Self's. Theirs might be exactly like yours, or they might be completely different. It depends." 

There was a brief pause as their teacher looked around the corner before he led them to the empty street. 

"There are four different types of Other Selves." He held up his hand with one raised finger. "One; those who are the exact opposite. These will not even look like you, besides basic body type. They have the complete opposite personality, quirk, and values that you have." 

Another finger raised. "Two; those who are repressed. These look like you, and might even act like you. But their values and traits are those of yours you repress and-or push aside. They might not even be actual traits you have, just things you don't like and have shoved to the back of your mind. These usually have your quirk or a somewhat warped version of your quirk." 

One more finger. "Three; those that you could have been. These will look similar to you, usually, but their personality is different. They are the you that made different choices, they are the you that didn't get to where you are, and if they did they didn't get there how you got there. Their quirks are always the same, but their outlook on things and how they handle themselves are different." 

The last finger he would raise. "Four; those who are a mix. They could be any combination of the first three. They are very rare, and I think Nightmare has only had a handful of these cases." 

Aizawa looked over his shoulder. "That's all." 

The students broke out in quiet murmurs as they watched their surroundings. 

There were all sorts of questions going around, only one student wasn't participating in the least. 

Midoriya. 

He was terrified, green eyes wide as he glanced from each building, back to his teacher, then kept moving his scan further. 

He didn't know what to expect, and for the man who planned out how to deal with any quirk he might come across, that was anxiety inducing. 

As they turned down another street, the buildings a mirror of those in their world yet without the flashing lights, screens, and signs-or even a single car, they all stopped in their tracks. 

A sharp giggling caught their attention, echoing off the surfaces of the buildings and ringing in their ears. Bright, high pitched, and slightly manic . . . 

They fell into a fighting formation; Aizawa, Todoroki, Bakugou, Midoriya, Iida, and Yaoyorozu made the outside ring of defense. The others readied themselves, each taking up a post behind the their teacher and the top five of their class. 

"Aren't they just so cute!? Look at them!" The giggling voice echoed again. This time a deeper chuckle joined in. "Oh, so pretty! Can I go see her now? Oh, please say I can!" The giggling turned to whining as the voice pleaded. 

"You know what the boss said. We can't risk it. There are others to face them first." The deeper voice chuckled again. "Come on, Love, we've got to go." Then the giggling faded away before disappearing completely. 

"Okay . . ." Ashido giggled nervously, drawing out the vowels of the word. "Anybody else find that super creepy?" A few of the students raised their hands while the others just shook their heads at their friend's antics. 

"Come on." Aizawa grunted, moving the group forwards. "We have to keep moving."