Musutafu, Japan...
It had been a long battle, All for One's successor, Tomura Shigaraki (previously known as Tenko Shimura) had devastated an enormous chunk of Hosu City, where Izuku Midoriya, Katsuki Bakugo, and Shoto Todoroki lay on the ground, gravely injured. All citizens had been evacuated to not get caught in the crossfire of clashing quirks.
"Some heroes you are!" Shigaraki shouted, laughing at the dying heroes, "You are the problem of this society, and I'll be sure to eliminate you!"
The heroes didn't reply. They couldn't reply. They were too weak from the battle they had with the decaying menace, Shigaraki. The heroes watched as he approached them with a twisted smile on his face, extending his hand to finish the job. Until...
"This isn't over yet!" Yelled an enraged, familiar voice from the sky.
What looked like a comet was approaching rapidly, crashing into the broken streets of Hosu. When the dust cleared, the shadow of a tall, muscular man was revealed.
"No! You're not supposed to be here!" Shigaraki yelled, in disbelief of the figure standing before him.
The three heroes glanced at the figure Shigaraki was staring at, being shocked by who it was.
"Do not fear, heroes. Why?" Said the figure, standing tall and proud, elbows extended, fists on his waist, with a big, bright smile on his face. "Because I AM HERE!"
It was All Might, in his golden age costume, looking younger.
"How!? You're weak! You lost your power against All for One!" Shigaraki yelled.
All Might smiled, closing his eyes, remembering Eri's words: "The world needs you! Deku needs you!" Eri used her quirk, rewind on him to revert All Might to his prime, causing One for All to return to him once more.
"Thanks, kid." All Might said quietly, then staring back at Shigaraki. "That's none of your concern. Right now, all that matters to me now is to save my students and end this. Once and for all..."
All Might didn't waste any more time, dashing at Deku, Bakugo, and Todoroki at blinding speeds, snatching and throwing them at a purple and black mist.
"That's... No! That traitor!" Shigaraki yelled, in sudden realization of who else was helping the trio escape.
Shigaraki didn't have a chance to tantrum further, being blown away by a gigantic gust of wind.
"This is between me and you, Shimura!" All Might yelled, dashing at Shigaraki.
Shigaraki stared at All Might, with an enraged look on his face. "Your efforts will be in vain, All Might!" He shouted, ready to end All Might's life here and now.
At the other side of the portal...
"It's good to have you back, Shirakumo..." Aizawa said to a tan-skinned figure with hair that looked very similar to the mist where the heroes were thrown to.
"It's good to be back, Aizawa!" Shirakumo said cheerfully, while Hizashi Yamada, otherwise known as Present Mic, was hugging him tightly. ...and crying rivers.
"I missed you so much, Shirakumo!" Present Mic sobbed, still gripping him with force.
"Still haven't changed, huh 'zashi?" Shirakumo said, patting Present Mic in the back.
Out of the portal came out the injured heroes, who were immediately taken to Eri, so they could be rid of their injuries. A few moments later, the three heroes returned to the battlefield to aid All Might. They, however, were not the only ones going to help.
"I never would have thought I'd say this, but thanks for your help." Aizawa said, talking to a black-haired man in a ninja-like outfit.
"I do this for a better, stronger society, and for the true heroes that have fallen victim to that pathetic excuse of a villain." Said the man, sheathing a katana, determined to put an end to Shigaraki's reign of terror.
With that said, the five stepped into the portal.
At the other end...
All Might had been struggling to stall Shigaraki's attacks, as well as try to land devastating blows to hopefully knock him out cold. All Might managed to land a hit on Shigaraki's stomach, making him bleed over his sides. The blood was caught by the anonymous ninja's blade, which was licked clean by its user.
"Why you...!" Shigaraki shouted, stopping mid-sentence as he felt his body suddenly paralyze.
Shigaraki fell to the ground, desperately trying to move. Only to receive a blade to his left hand, piercing it to the ground. Shigaraki moved his eyes upward, to see the hero killer, Stain, with Aizawa. Aizawa's eyes glowing red.
"Now!" Stain and Aizawa yelled at the four heroes, jumping back into the portal to avoid what was about to happen.
"Let's finish this!" Bakugo yelled, using his explosion quirk to lift himself in the air.
"For everyone!" Todoroki shouted, preparing his fire and ice quirk.
"For a better future!" Midoriya screamed, channeling One for All throughout his body.
"Go beyond!" All Might said in a battle cry.
"PLUS ULTRA!" Said all four heroes in unison, aiming their attacks at Shigaraki.
"Howitzer Impact!"
"Flashfreeze Heatwave!"
"Delaware Smash!"
"United States of Smash!"
All attacks clashed against Shigaraki, ensuring no remains of All for One would be left. A few seconds have passed. It felt like an eternity. When the dust settled, it revealed the four heroes on the verge of death, due to the massive firepower of the combined quirks. As All Might lost his last breath, he muttered with the little strength he could manage...
"You showed the world what being a hero means..." All Might said a weak, as his life hung by a thread. "...I couldn't have asked for a better class..." All Might stared at Deku. "...and a better successor..." All Might closed his eyes, leaving his consciousness behind.
As their bodies lost feeling, the four heroes mustered up a smile as their last message to the world, which was "No matter what the problem or situation, you must face it head-on with a smile!"
And there lay the deceased heroes, on the ground, clothes torn up, blood spilling at an alarming rate. But, they were smiling, as if they had won something great. Something that would live on through the minds of many generations to come. And so, the heroes rest in peace.
***
All Might, Deku, Bakugo, and Todoroki woke up in a dark, pitch-black abyss, confused. Wearing casual clothes. All Might wore the outfit he used when he saved Deku and Bakugo from the sludge villain. They noticed that there was a shining, white door.
"Where the hell are we!?" Bakugo yelled, pissed at not knowing where he is.
"Calm down Kacchan!" Deku said, trying to ease the raging blonde's anger.
The two childhood friends argued with each other, while Todoroki watched. All Might, however, was more intrigued by the glowing door. He approached the door, opening it to reveal a giant library with bookshelves filled to the brim with various titles and novels All Might had never heard of before.
One particular book that caught his attention was named "The Records of the Four Cardinal Weapons", which was sitting tall on a pedestal, covered by glass. The other three heroes followed All Might to the library soon after.
All Might removed the glass isolating the book from the pedestal, beginning to read it. He found out that the literature's contents held various information about four heroes and their respective weapons, those being: The Sword, The Spear, The Bow, and finally, The Shield.
He had gone through a majority of the book in little time, until he was stopped at the part of the shield hero, due to the pages supposedly containing his data being completely blank. So, he was unable to find any information regarding the mysterious man.
All Might was surprised to see this, getting startled as he saw the blank pages begin to glow. The trio of students rushed over to see what was going on, only to be engulfed by a bright light. All Might woke up once again, this time in a different place. He could faintly hear voices say:
"The summoning worked! Please help us protect our village, heroes!" Said various voices in unison.