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Everyone knew how Pietro was so overprotective of his sister. He was an okay guy most of the time, especially when he was exchanging jabs with Clint (even though he was a higher ranked agent) but not even Black Widow (and some even claimed that Director Fury, too) would stop him from unleashing his brotherly wrath.
The Black Widow incident occurred when the Russian agent landed a kick on Wanda as they sparred and in a blink of an eye, Pietro had already pushed their instructor off and banging to a wall. Natasha was pissed and Pietro was punished for his insubordination and recklessness. Wanda was frantic and worried for her brother but reprimanded him for being too impulsive.
Before the Black Widow incident, mostly the other guys just laughed it off and teased Pietro. The speedster, so as long as no one laid a hand or made a stray insult to his sister, merely laughed it off until everyone stopped making a joke about it except Clint or when Tony dropped by on rare occasions.
No one really thought about it now, but they did make an effort to not do anything that might set off Pietro on a rampage.
Then a confrontation between Pietro and another agent happened. No one remembered why or how it started but they suspected it had something to do with the last cup of pudding. Pietro was a good fighter who used his unnatural speed to his advantage but a carefully calculated punch sent him back and falling, knocking the wind out of him. There were cheers and nays that filled the cafeteria, laughter and boys being boys.
The agent was just about to grab Pietro by the shirt when he suddenly stopped and froze in position, strings of red light forming around him.
"What're you doing with my brother?!"
Everyone turned to the Scarlet Witch, eyes red and her hair floating around her. She suddenly looked like she stepped out of a horror movie, complete with the murderous intent on the agent now suspended on air. Bystanders held their breath as Wanda marched in, glare on her usually kind face. Then flicking her hand, the agent was sent flying several tables back, knocking down plates and food. He was pushed to the wall, trapped between it and what had previously been one of the steel tables now a contorted mass of solid that held him in place.
Wanda came to her brother's side, he'd laid there on the ground as if truly injured, and helped him up. She glared at everyone else, causing them to flinch in fear of being subjected to her strange powers, and helped her brother out to the infirmary.
Since then no one messed with either of the twins in fear of the other. Though Clint (or Tony) would sometimes go overboard with their jokes and teasing and they usually found themselves slammed to a wall with red lights as if holding them in place.