Aizawa noticed the portal and screamed out to Thirteen to protect the children. He yelled out to the students to huddle together and not to move.
Aizawa: DON'T MOVE!!! THOSE, ARE VILLAINS!!
I heard the conversation that they were having as they emerged from the portal, but it was not as if they were keeping quiet about it.
Kurogiri: Eraserhead and Number Thirteen… According to the teacher's curriculum we procured yesterday Mr. All Might was supposed to be here, and yet…
Aizawa: I knew it. So yesterday was the doing of you louts…
Shigaraki: (In a raspy voice) Where is he?! We went through all this trouble and rustled up so many of us to bring along…You can't tell me All Might…The symbol of peace…Isn't here!! I wonder if he'll show up if we kill the kids?
I know if taken in a different context my giant smile would be seen as either obscene or inappropriate but after recovering and training I welcomed the blood I was about to spill on my hands. The kids were panicing because to most of them, this was their first encounter with villains. The few that were calm were Midoriya and Bakugou as they already had a run in with a minor villain, the sludge villain. Aizawa jumped in to fight the group of villains by himself while Thirteen was protecting the kids.
Shigaraki: God, Pro Heroes are such a pain. If we were just any rabble, we wouldn't stand a chance.
Midoriya: Incredible! I forgot that one-on-group battle is Sensei's specialty!
Ida: This is no time for analysis! We've got to evacuate!
Kurogiri: I'm afraid I can't allow that. Greetings. We are the Villain Alliance. I apologize for the presumption but we took it upon ourselves to enter UA academy, the base of Heroes. In order to engage with Mr. All Might, the "Symbol of Peace." We were wondering if we might be allowed the opportunity to extinguish him, you see.
Thirteen was about to attack him but the kids attacked first. When they did attack, Kurogiri spread his gaseous type body around the group and portaled them around the training areas where other villains were ready to ambush them. In order to stop the villains from retreating, Kurogiri needs to be the first to die. After the kids disappeared, I grabbed Kurogiri by the armor neck guard. Despite him being gaseous that was his only solid part that was considered a weakness.
Sage: Ms. Thirteen. I will take care of him and help Aizawa-sensei. Go help the children.
Thirteen: (Shocked at my presence) Uh, yes ok.
Kurogiri: (Trembling) Who… are you?
Sage: (With a big smile on my face) To the kids, Sensei, to the other teachers, co-worker, but to you lot, I am death.
Kurogiri: I thought you Heroes were opposed to killing.
Sage: Truthfully, I waited until you continued to add to your crimes. First: You broke into private property en masse. Sure that is not enough to warrant death, but second: You broke in with the malicious intent of murder and lastly you put under age minors in harms way, plus if any of them get hurt that will be another charge.
I looked at Aizawa who started fighting Nomu and got his arm broken.
Sage: See, another crime. Since everyone has a quirk, we are technically biological weapons so we can consider Aizawa-sensei's arm broken as aggravated assault with a deadly weapon. A crime within a crime on top of a crime with a crime on the side. With the grand entrance you made led me to believe that if shit hits the fan for you, you are the person for the bail out. So, goodbye Mr. Fartcloud.
Kurogiri: NOO…!!!(Choking noises)
I squeezed the metal armor neck plate with a Haki covered grip, killing Kurogiri on the spot. For good measure, I held a seemingly dead Kurogiri in my hands and created a miniature sun to burn the remains. No trace was left. I flashed down to Aizawa and stopped the Nomu before it smashed Aizawa's face in the ground.
Sage: Hey now, let me have some fun as well, Aizawa-sensei.
Aizawa: What the hell took you so long?
Sage: (With a serious expression) Do you want an honest answer or small banter?
Aizawa: An honest quick answer!
Sage: You're no fun. I just waited to justify killing them.
Shigaraki, Aizawa, Midoriya, Tsuyu and Mineta, who just came back from subduing the villains they faced, were all shocked by my answer. The kids were trembling in the water, as they looked at my expression. I was a little bloodthirsty as I waited for this day to come.
Sage: So, this is the artificial human, Nomu? I'm guessing that even chopping its head off won't do anything because the brain is exposed, so it's only decorative.
Shigaraki: Who are you? There was no mention of another Hero other than Thirteen, Eraserhead and All Might on the curriculum.
Sage: Haha, I'm only a temp. So you and your jazz hands can hold your applause.
Shigaraki: Nomu was created to stop All Might and you are no All Might, so he will make quick work out of you.
Sage: I don't see where your confidence is coming from. If your jazz hands weren't obscuring your view you might see better. There is super little to no effort holding your love doll in place here.
Shigaraki looked again and his eyes nearly popped out of his skull. I was stopping Nomu with my right index finger pressing against the space between his eyes, but not on the brain, don't want none of that brain matter on my hand.
Sage: Even All Might would not have problems with this thing, well now he won't. Yo, Midoriya, get over here and deal with thing, it should be around your current level.
Midoriya: Hai!
I grabbed Tsuyu and Mineta telekinetically to put them away from harm, but close enough to watch. Midoriya ran and tackled Nomu away from me. I turned to Shigaraki and walked to him. Shigaraki grabbed my arms and gave me a giant smile.
Shigaraki: HAHAHA!!!! Let me give you a little information about me, whatever I touch will crumble and decay! Prepare to die!
Midoriya: Sage-sensei!!!
Sage: Midoriya, stop shouting and focus on the Nomu.
I felt Shigaraki's quirk as my arms were weakening a bit but more of an irritating itch. I was healing faster than his quirk could do damage so it looked as if he did nothing at all except made the sleeves on my shirt fall off.
Sage: Awww, is that all?
As Shigaraki's eyes were widened and fear set in, my smile became more vicious. I quickly grabbed his arms above the elbow but below the shoulder and easily snapped his arms. Shigaraki made a horrible scream. If his voice was raspy before, now it would sound as if he smoked 5 packs of cigarettes a day for 40 years. I didn't stop there, I quickly poked his legs above the knee but below the hips to break his legs. I made him watch as Midoriya trained with the Nomu.