Sans sighs as he walks the pathways and halls down to the classroom, rubbing the in between sections of his eye sockets and looking back towards Frisk. Now that hes..well, relaxed...at least he knows the kiddo ain't gonna do anything to him, but...Chara is a wild card...more or less a villain in her own right, if she didn't pull that same card she always did per conversation. He'd confront her every now and then about her reasonings with committing genocide..she really always gave the same answer, yet it somehow made sans seem understandably untrustworthy of it. He sighs, decidedly turning around to Frisk's surprise as he looks to Chara

"....so why'd you do it?"

Chara cocks her head, looking around before folding her arms, sighing in contempt

"..is this about the timelines? The genocides, Sans? You already know the answers to those questions. You've asked them soooo many times down in the Hall...yet somehow, you'd think I'd lie to you?"

Sans sighs as he adjusts his jackets hood, walking still down the hallways

"..I mean seriously...you always say it's a rush doing all these things, yet you've done it so many times, it's becoming predictable...yet you press on. Every single timeline, you'd do the same thing...over and over again. Nothing ever changes, yet you expect it too..or do you? Is there some ulterior motive I'm missing here now this timeline exists? A timeline where you want to do something different so that you can get bored of it and resort to genocide?"

Chara floats there for a moment, remaining silent for a bit before sighing

"...I've already answered your questions, Sans...every time you ask, you'll get the same answer. It's hypocritical of you to say I'm repeating the same thing when you knowingly follow suit..and ask the same questions. Over and over again."

Sans sighs as he walks the corner, the classroom in the corner of his eye. He intentionally missed that classroom for a bit to get adjusted to the situation at hand, before sighing and scratching his skull

"....I guess I am a hypocrite...maybe I'm just some unworthy judge, maybe I'm some smiley trash bag who cares for no one but himself..but your worse. You've done unspeakable acts and knowingly committed to it over and over. So don't you ever say I'm worse off. Because at least I fight for a timeline where it's a happy ending for us...one that I at least have a family to go back to."

He sighs as he opens the classroom door with that word to make Chara shut her trap.  As he walks in, the classroom was staring at sans, then Frisk, and then Chara. Aizawa was already leaned back on his desk, his breath calm and tired as he opened his eyes

"...your late..."

Sans froze and mentally yelled at himself, before Aizawa sighs

"..is what I would have said if you remembered that class ended with AllMights instruction..but...of course..I told the class while you and your...."friends"....took a detour, and told them to come to class after the lessons...for one reason."

He soon turns around and walks to his seat on his desk, soon kicking back his boots up to it and sighing

"...so...Sans, right? Or is that some anagram or other pen name you use to hide your past..? Either way it's not my business..but..you at least deserve to give an explanation to that scene you gave earlier...your hyperventilating, upset mood....never really seen you act that way before."

Sans sighs as he gently rubbed his skull, soon walking up to the front of the class, and sighing

"...well..ain't that peachy...well..I suppose it won't matter since Frisk can't..Reset."

The students gave a relatively puzzled look, a few mumbling over what a "reset" even was. Frisk was a bit shocked to say the least..sans never not once talked about her power..but fully understood that she also never seen anyone confront him with the knowledge of that said power.

Sans sighs as he soon paced around the room, thinking of how to appropriate his words carefully.

"...me and my...friends...aren't from this place..or, well...this timeline. I'm sure a few of you understand the concepts of space time, alternate universes, timelines, etc...for a basic run down, in this Universe, you are training to be heroes...in another, it could be quite the opposite..."

He sighs and rubs his temples a bit

"..in other words, I'm not from a timeline like this...where I come from...there ain't no magic powers...there ain't no perfect symbols of peace...we have to do what we do on our own, with what we call magic."

The classroom seemed intent to listen into this. Sans sighs as he takes some chalk and writes on the board a crude drawing of a monster and a human

"...in our world, there were two races..humans and monsters. Monsters had weak magic...but humans had stronger wills, Magic, and even determination to assist them...our souls shatter if we die...while human souls persist..."

He sighs a bit and draws a barrier on the board

"..humans never trusted our kind..I wasn't alive back when the war happened..but accounts from our king and queen told us it was devastating...of course I knew it had to be, since it was a war and not some small skirmish...but..it happened. We were banished to the Underground and forced to survive down there..wasn't bad for the most part..me and my bro sort of adjusted to our new home in a nice snowy city.."

He drew a crude image of Papyrus yelling at him while he was passed out on a couch

"..he was always so serious and all that...uh..anyways...back to the point.."

He sighs and rubs his eye socket

"...a human fell into the Underground..her name? Frisk. First go around, she was an innocent and fairly confused individual...I thought she'd either die or leave..either way I'd watch them...till the end. She spared the King but...let's just say a certain flower had their way...long story short..she left."

He sighs a bit and soon writes a few scientific formulas

"..felt like I woke up from a nap..one moment I was watching the human leave the underground, and calling them, telling them we know she'll free us..then...poof. I woke up in my bed again..and apparently she had a certain power..she could reset a timeline to a point, or even the beginning, If she ever so wished...she pulled another timeline and managed to befriend everyone..then..after a fight with a depressed prince...everything was back to normal.."

He sighs as he watched the students seem to pay more attention rather than chat and act as if this was nothing. Izuku seemed to pay even more attention, taking notes and recording the formulas he made

"....then the timeline reset. Again and again, we'd get a happy ending..only to come back. Turns out, she felt...lonely. But soon, she realized that once she saw and heard everything..she grew..bored, oddly. She soon found out that she could truly reset the world, blah blah blah...she did. I had to go through it all again, but..it would have ended happily, till..well, she wasn't the same."

He sighs and looks over to Frisk

"...she wasn't acting like her usual self. Every step seemed calculated by someone or something else...she was always dusty...her speaking became less and less..and then..she sort of lost that light in her eyes."

He walks to Chara, his eye sockets growing dark

"...mind tellin' they why, buddy?"

Sans walks away from Chara, with her sighing aggressively as she soon sits on his desk. Aizawa didn't seem to mind, only taking his feet off of it to watch her

"...I killed them. All of them."

The class sort of collectively froze, they're faces contorting from confusion to fear

"...yeah. There's no use beating around the bush anymore..Sans always does that...expecting maybe he could just say a life story and expect people to change in a matter of moments..well, he must have realized that in the end it didn't really matter..."

She soon steps on the ground, soon smiling a bit

"...I grew bored of certain aspects of watching a timeline fall over and over...I convinced my partner here to accept my little offer...see what sort of timeline that could happen if they killed everyone...of course it was indirect, mainly pointing out very minute details with the same quotations, like "you already know what they will say" or "you already know what your going to have to do" and..well, she noticed."

She raised her arms and shrugs

"..with time, she became tempted..she'd kill and hesitate, never liking it..until I took over. Over and over, every kill, I took more control...until finally, it happened...a grand open hallway with yours truly at the end. Our own personal judge."

She bows and laughs a bit, pointing to sans now. He sighs as he leans against the wall

"..of course he could have done things differently but..that timeline made him weak until I reached a point...then he sort of cheated out the timeline over and over. But he was as tough as you see him..constantly playing around with his opponents till with a single flick of his wrist, absolutely destroy you."

She smiles and walks to Frisk, gently taking her shoulders

"My partner received a whooole lot of punishment..but she learned...ain't that right?"

Frisk uncomfortably nods as she folds her arms, shrinking into her own corner

"..of course, I was ecstatic when my little partner finally slashed that smiling trash bag right across his chest..he looked pretty weak then..I mean, one hit surely did a number on him...even did beyond his bodily limits..he held on for a few..but gave up in the end."

This class collectively backed their heads up, seeing how truly psychopathic Chara was. Aizawa was even afraid of this girl, wanting to pin her with his scarf and put her away forever...if she was not only intangible, but also required for Frisk to even survive.

"..well..in the end, it happened a few hundred resets..over and over, id learn the patterns, and feel relieved when I did the work then, seeing and feeling the adrenaline course through her veins as I cut them down....strangely though, one reset later, me and her woke up in a trashy allyway..timeline must have bumped into yours and we just got in along with sans. Now that I have this timeline..."

She gave a devilish smile, seeing everyone collectively almost jump out of theirs seats to escape, knowing that this...thing...couldn't be killed.

"...I wanna see what's here to offer...see the sights, the sounds, and all that. It's new. The timeline doesn't even seem like one that is predictable...rather than plain archetypes, everyone in their right minds are purely human..so if your so afraid of me, sure, just do that...but...I never lie."

The entire class looks back at sans and frisk for confirmation, with both giving a disappointed nod. The class were still apprehensive though, with Bakugo slamming his fist on the table and standing up

"..your telling me we're harboring a Goddamn brat whose committed murderous acts..yet your just gonna let that bitch get away with it?!"

He yells at Aizawa, him standing over his desk as Aizawa sighs

"...we...we can't exactly incarcerate a ghost...and with the apparent fact that this girl is tied to the more innocent one...and the fact they'll both die...and the fact that everyone from said world is saying she never lies, and considering sans has encounter constant timelines with her..."

He sighs and folds his arms

"...we will keep her under heavy surveillance...every move we will watch..if she goes as far as to harm another hair on anyone's head with the intention of death..."

He inhales and sighs

"..we will have to incarcerate Frisk in order to properly contain her."

The class sits there in shock, seeing that a seemingly innocent young girl would have to suffer for the worlds sake...even Chara and Sans gave glances of absolute disbelief. They could understand heavy monitoring, they could understand why they wouldn't go as far as to kill frisk, but..to end up entrapping her?

"...T-thats...thats isn't fair for Frisk!"

Izuku and sans said at the same time, with Chara reminding silent

"..Why the hell does the kid get punished? Ain't that social injustice?"

Aizawa sighs and walks to the door of his classroom

"...we're sorry. But Chara is too much of a risk to be taken lightly...not only does she show no remorse for her actions..but she actively acts like yours and many others lives were some game..in the end, we have to take measures if Chara commits those acts..."

He walks out the door, simply saying two words

"Class dismissed..."