3rd POV:
It didn't take long for Izuku and Dabi to arrive at the warehouse and meet up with Stain. In fact, both of them needed to wait for Stain since he didn't know Dabi and was checking them out first and making sure that no one was following them and this was no trap. Once he made sure of that he landed in front of them and picked Izuku up.
Stain: Ah, long time no see kiddo!
Izuku: Hey Stain!
Dabi: PUT HIM DOWN!
Stain somewhat found himself worrying about Izuku after hearing how he felt about the world. Just the small amount that Izuku was talking about All Might was enough for the hero killer to know how much he despised the fake hero and that alone was all he needed to know. For Stain the little green bean was felt somewhat like a small brother he never had. A kid he wanted to protect for once in his life. He was no father and he knew that so he decided he would act as his older brother at least and watch over the boy from the shadows.
Dabi on the other hand was jealous about Stain picking Izuku up so casually and showed his flames the hero killer warning him if he was not to put down Izuku immediately he would have attacked him. Not wanting to risk Izuku getting hurt at all he put the small bean. It might have been that or the angry ferret hissing at him.
Stain: I have checked what you told me about the number one hero and I found it to be rather true. As unforgivable as it is, he needs to be eliminated.
Dabi: Fuck yes!
Stain: This however is not a job for a kid and a wanna be hero!
Dabi: The fuck are you calling wanna be hero! Just for your information, I am Dabi!
Stain: Oh so you are the kid that does everything for money.
Dabi: Did. Izuku gave me a new life.
Stain: A true hero by heart, I see.
Izuku: Well he saved me from a villain attack too but enough of that. Now let's chat about how we will get rid of the number one.
Stain: We?
Dabi: Hell yeah!
Izuku: No, Dabi!
Dabi: Why not?
Izuku: Because of our parents and just imagine if they find out that two kids got rid of the number 1. They will skin us!
Stain: He is right. This is no job for you two. I will take up this burden.
Izuku: Which reminds me of why I said we.
Stain: ...
Dabi: ...
Izuku: Me and Nezu came up with a plan in order to get rid of the number 1. I have gathered a lot of information about him and here is what we both got so far.
Dabi: How long were you planning this?
Izuku: Long enough and it is the first step towards my goal after all.
Stain: Your goal?
Izuku: A world without any discrimination, where everyone can be what they want to be and no one telling them that they are made to be a hero or a villain. The whole concept is old-fashioned. People are not villain for nothing. They were made by others even forced to be ones. No one deserves such life.
Stain: I see. A noble goal, which I shall assist you!
Dabi: You do realize he is talking about world domination right?
Stain: If this is the path he chose then I will be following him!
Izuku: Thank you!
Dabi: So what did you find out about the hero?
Izuku: First of he can only be in his buffed form aka muscle form twice a day. In this period, he is able to use his quirk however he wants but once that the time is up, he will be in a skinny form and rather weak.
Stain: That is some deadly information you have there.
Izuku: I have more.
Dabi: I am proud to be your brother!
Izuku: His real name is Toshinori Yagi. He lives in the apartment in the ********** street house 13 door 6. I had Nezu watch over the hero the whole day and so we know that he already used up all his time as a hero. If you had to attack this is the best opportunity.
Stain: That is indeed the case.
Izuku: What's more, he also has an injury on his torso from a passed fight which couldn't be healed completely. If you hit him in the stomach hard enough he should start coughing out some blood and he would be weakened.
Stain: I will be keeping that in mind.
Dabi: Do you also know his favorite color and foods too?
Izuku: Yellow and he likes Miso.
Dabi: I was just kidding but you were not joking when you said you gathered a lot of information about him.
Izuku: I never joke.
Dabi: I wouldn't wish to be your opponent.
Stain: Capable and intelligent that is one good combination you have there.
Izuku: Thanks I guess.
All of the sudden Dabi's phone went off and he went out of the building in order to talk with his parents. It was Mic to be precisely. He wanted to inform them that he would be getting home early. This meant that both of them had just 30 minutes to get home. Knowing that Dabi went back in.
Dabi: I hate to break it but Mic just called. They will be at home in 30 minutes. We need to go, Izu!
Izuku: Okay. Well see ya!
Dabi: Till next time!
Stain: Bye.
Just liked that the two brothers left the hero killer back alone. With all the information he just gathered it was a guaranteed success. He was considering himself lucky meeting Izuku and being on his good side after hearing what he could manage to gather about the number one hero. Just imagining what the kid could do if he wanted to go after a person himself send a shiver down his spine. It was the first one in a long time that he realized how fortunate he was. Nothing could stop him in trying to stay on the good and safe side of Izuku. Something told him if he ever was about to make an enemy of the kid that he would be dead meat.
Stain: Now, ket's go to work!
With that he exited the abandoned building and made his way over the rooftop towards the hero's side. It surprised him to find a man in the room that almost looked like a walking skeleton. Now he knew why Izuku referred to his condition with skinny form and bulky form.
It was surprising easy to have a look through the window from the rooftop of the other building. There was no doubt in Stain's mind that the man in the apartment was All Might himself. Knowing that he had two forms, he could see how identical both people looked alike. The same hair, the same bunny hair strain and then the color of his eyes were the same too. Even the height of the person was identical.
Once Stain was sure he had the man, he went to the other side of the rooftop and started running back towards the house All Might was in. His goal was to enter the apartment through the window. With that in mind Stain began speed running over the rooftop and jumping off it, covering his face with his arms and letting himself fall through the window and rolling himself on the impact.
Not only was he now standing in the apartment but he also took out his knife and ran at All Might. The poor hero was surprised by the attack and didn't had enough time to use his quirk or react at all. Even if he wanted to use his quirk he would have only had seconds in his buffed form.
Stain: Your time is over fake hero!
That was all Stain had to say before charging at the man. The hero was able to dodge some of the killer's attacks but not to the fullest so that the katana managed to cut him.
Stain: This will be your end.
Just like that he liked the blood and used his quirk to enable All Might from Moving. That was the heroes end as Stain stabbed his sword through his heart from the back. All the fake hero could do was cough up some blood before stop moving completely.
Then all of the sudden some police sirens could be heard and he knew that someone must have informed the police because of all the noises that was going on and so he quickly left the crime scene.
The police came rather quickly and went straight to the apartment of the hero. It was Nezu who informed the police about the incident after he made sure that the hero killer was done. All Nezu did was hacking into the security camera footage of Yag's home and watch the whole movie. The rat even had some popcorn and some good tea while he was watching the whole fight unfold.
After the fight was over, he decided to call the police and tell them that he found some evidence believing that a villain was about to attack All Might after all the rumors going on. Naturally he knew who was attacking who and when. Not to mention that he was one of the people spreading words around about All Might's weakness.
In addition to calling the police, he made sure to take Recovery Girl with him in order to assist the medics if there was any chance of 'saving' the hero. Being quite honest, there was no chance of the hero to survive from the beginning. This was all an act he needed to pull off.
Thankfully no one questioned the rat or how he knew anything he knew. With that he was able to get into the apartment and have a look at the corpse. He then let Recovery Girl get some DNA strains as in getting his blood secure and a hair strain too before leaving.
He then told the heroes that this looked like a villain that was trying to imitate Stain's work. No one questioned the words of the all mighty Rat SATAN again. This was how the first step of world domination went smoothly without even a single problem at all.
No one suspected Izuku, Dabi, Stain or even Nezu to be the main culprits behind this attack.
No one knew what was still about to happen.