2 days later...
A few days have passed since Izuku learned how to make the Rasengan. He noted that he would only use that technique unless it's his final resort due to the amount of power it releases and the number of drawbacks it can cause Izuku's arm. Right now he's currently packing his bag, getting ready to return to Japan.

"Come on dude, can't you just stay a bit longer?" Mikey asked with a sad face.

Izuku closed his eyes as he remembered when the news report mentioned that the Hero Killer attacked Ingenium and how his brother was having a face of revenge on his face at the train.

"Sorry, but I have a feeling something bad's gonna go down back home," he said as he looked at the hand he performed the Rasengan with which was wrapped up in a bandage. "And I'm gonna be the one to stop it"

The turtles couldn't help but feel proud of him. Izuku summoned his Odachi, concentrated on the train station he took to the airport, and opened a portal.

"Well, I'm off guys," he said. The brothers held out their fists in respect and Izuku held up his. 

"TURTLE POWER!!!!!!" Izuku shouted as his suit came out from his ring. At the same time, he jumped into the portal until he landed in a bathroom stall with a foot in the toilet.

"Guess I should've thought more carefully about where to land," he said while laughing behind his mask.

As he stepped out of the bathroom, he quickly hid behind a pillar when he saw someone he didn't expect. He saw his younger twin sister walking with a little old man wearing a yellow suit.

"Crap, why'd she have to be here at the same time? And who's that person with her? A pro?" he said to himself.

"Now boarding the next train to Shinjuku Station. All passengers please board the train," the person on the train station P.A system said.

"Shinjuku Station? It's gonna go past Hosu City. Perfect," Izuku whispered as he jumped onto the train.

"You gotta be kidding me?" he said to himself as he saw Izumi walk into the same train he was in. He chose to shrug it off as the train started to depart.

During the ride, Izuku lay on top of the train while playing a game on his phone. He chose not to tell Ochaco that he was back because he wanted to save it as a surprise. Suddenly the train came to a sudden stop.

"Wh-What the hell was that!?" Izuku said as he slipped on his mask.

He got his answer when he saw a recognizable creature rip the side of the train.

"Another Nomu? What the hell are the league up to?" he said as he summoned his Katanas. Surprisingly the old man who Izumi was traveling with came and kicked it in the face causing it to fly away. As the old pro began to chase after it, Izuku took the chance to observe his surroundings. He was in the city he was aiming for but it was in total chaos.

"I gotta find Ingenium's brother fast," he said as he jumped off the roof of the train.

Using his speed, he jumped from rooftop to rooftop until he heard screaming from an alleyway. He followed the scream until he spotted 3 figures. One was a pro hero, the other was Ingenium's brother due to his costume and the other was the Hero Killer himself holding a blade over the student.

"Oh shit," Izuku said as he jumped off the roof, activated Tech-Jutsu in which summoned his bo-staff and smacked the Hero Killer in the face. Iida took the chance to look up at his savior.

"Hey, are you ok?" Izuku asked Iida who was on the ground.

"You, you're the one from the USJ attack. Carapace," he struggled to say.

"Yh. I heard what happened to your brother. Telling that you're here, you must be out for revenge am I right?" he asked.

Iida gritted his teeth as tears began to come out of his eyes.

"I have to. I have to live up to the Ingenium name and kill this monster. So get out of here, and let me do this," he yelled.

Izuku sighed at what he said.

"If your own brother was here right now, do you think he will happy to see his own little brother living up to the Ingenium name by covering it in Stain's blood?" Izuku asked causing Iida's eye's to widen in fear. Stain got both their attention when he got up after being knocked by Izuku's stick.

"Ah, I heard about you. Your that young ninja vigilante. You know, we're kinda like you and me. How bout you join in bringing justice to these fake heroes," Stain said pointing his sword towards the hero Native. Izuku in response switched from his Bo-Staff to his Twin Katanas.

"I understand what it means to bring justice. But you, you're just a psychotic monster. And I'm gonna be the one to stop you," Izuku said as he dashed towards the villain at blinding speed causing both him and Stain's swords to clash with each other.

"Yes! This proves you're worthy to fight me!" Stain said as he struggles against Izuku's blades.

"Worthy my ass!" Izuku said as he continued to fight Stain. Each time they clash swords, they would give each other scars or slash bits of each other suit.

--------------------＼(((￣(￣(￣▽￣)￣)￣)))／--------------------

Izumi was currently running through the city while looking at the destruction.

"This is crazy," she said looking at her surroundings. Suddenly she heard the sounds of swords clashing in an alleyway. She walked slowly towards it and took a peak, to see the Hero Killer himself fighting the green vigilante.

"Stain and Carapace!?" she asked herself. But her attention was brought to Iida was lying on the ground beaten up.

"Oh my god, Iida," she said as she activated full cowling and rushed over to his injured classmate.

"Izumi, you're here too?" Iida struggled to say.

"Yh. Hold on, I'll get help," she said as she took out her phone and sent out an S.O.S to all her classmates telling them what's happening and where they are. She then felt Iida's hand grab her arm.

"You gotta help him take him Stain," Iida struggled to say causing Izumi to look at the two swordsmen clash with one another. She nodded as she activated Full Cowling, jumped from one wall to another, and punched Stain in the face. She then stood beside Carapace in a fighting position.

"Thanks for the assist," Izuku said dusting himself off.

"No problem," Izumi said as she observed the vigilante standing beside her. Her eyes widened when she noticed pathers of green hair poking through the rips of his mask. "It really is you big brother"

As Stain got up, he noticed the two teens standing in front of him.

"You! Stay out of this you unworthy hero," Stain remarked.

"Like hell I would," Izumi retorted back.

The two siblings dashed towards the villain at blinding speed. They were so fast, Stain couldn't really see them.

"WHAT'S HAPPENING?! I CAN'T EVEN FOLLOW THEIR MOVEMENTS!!" he shouted seeing green streaks all around the place.

Suddenly he felt a punch to his stomach and a smack to his face by what felt like a stick. Their speed even impressed Iida. The attacks kept going until Stain slashed his sword cutting Izumi's legs. As soon as he licked her blood of his blade, she froze and fell to the ground.

"What the hell? I can't move," she said as she struggled to get up. Stain slowly walked up to her due to her injuries.

"Now, you die!!!" he shouted as he raised his blade to her. As he strikes down, Izumi closed her eyes in fear. When she didn't feel anything, she slowly opened it to see something unbelievable. Carapace was holding the blade with his left hands. She could tell he's hurt due to blood dripping from it.

"Listen here. Until I make a name for myself as a hero, I don't care what happens I'm not gonna die!" he yelled despite the pain he's feeling. Both Izumi and Iida were shocked by his words. 

"YOU BASTARD!!!!" Stain yelled as he was about to use his other hand and reached for a weapon. Unfortuanetly Iida was able to get up due to recovering from the paralyze. He used his engine to boost himself to the villain and latch himself onto his hand to prevent him from grabbing a weapon. Carapace took this as a chance to attack.

"Alright! Here I go!" he shouted as his Hamato eyes turned green. He began moving his finger on his right hand in a circular motion to cause the energy to move around into a ball.

"What the hell is that?" Stain said seeing the green orb in his hands. The two students marveled at the sight as well.

"Compress the energy! Keep it going!" he said until it thursted it into Stains chest.

RASENGAN!!!!!!!!!!!

Stain screamed in pain from the attack until he was launched into the wall. He laid limp their not being able to move. Iida, Izumi and Izuku who was holding hand due to the strain, walked up to him. 

"You, I always thought All Might was the one whos worthy to fight me, but I was wrong. Carapace, you're the one who's worthy enough to kill me," he wheezed out of his mouth before passing out with his mouth open. Izuku shook his head not wanting to go that far.

"I guess when you use that attack on him, it caused his ribs to punch his lungs," Iida said holding where Stain stabbed him.

"IIDA!!! MIDORIYA!!!" the 3 of them heard at the entrance of the alley. They could see some of their classmates and some Pro Heroes running towards them including the #2 Pro Hero.

"Look, it's the Hero Killer," Kaminari said pointing at the villain.

"and Carapace," said Todoroki.

"2 in one day. I got this," Endevour said while running.

"Guess that's my cue to leave," Izuku said as he summoned his Odachi in his left hand, open a portal and escaped through it leaving Izumi and Iida to explain what has happened.