(I'm not writing the coughing and wheezing because that would make reading it annoying. Thank you for your understanding.)
"When I was born, Quirks were just emerging. They were relatively new and not even called Quirks, but Meta Abilities. We expected super heroes, but mostly got petty thieves and villains with more power than they deserved. My brother, Yoichi, and I had never even come across someone with a Quirk until we were teenagers. Don't ask how old exactly, I've forgotten that long ago, but we were walking home from school and got cornered by an older classmate and his posse of goons.
The classmate had a Quirk that gave him the ability to create flames, not that we had ever seen him do it. His Quirk was nothing strong or special, merely a drop in a lake compared to some Quirks that exist today, but it had gained him popularity and fear throughout his social circles. He cornered me and my younger brother and demanded we pay him a toll for walking through his alley or he would burn us. We gave him what we had, of course, and then he laughed. He told us that we only had enough for one, and that I needed to pick which of us got burned.
I chose myself immediately. I was the older brother and it was my responsibility to take the hit, but as soon as I said to burn me and let my brother go free, his goons grabbed me and faced me towards my brother as the leader approached him.
I realized what he would do to my brother, so I shook his goons off of me and ran at him, tackling him and wrapping my hands around his throat as I tried to protect my brother. That's when I noticed an intangible… thing inside of him, sorry it is hard to explain what Quirks look like. I mentally pulled on it and found that it came with no resistance, shooting from him to me. It was then that he tried to use his Quirk and had a look of shock on his face when nothing happened.
I would rather not mention what I did to him in my anger, but by the time I was done his gang belonged to me and I vowed that I would never let harm befall me or my brother.
I was banished from my house, tossed out by my parents for being a 'freak', and my brother followed me to my new gang's favorite hangout, an old warehouse that actually used to stand in this very location. Call me sentimental, but I thought it would be poetic for the end of my influence to be in the same place as when my power was born. It was then that I proclaimed that I was All For One, and only my brother could call me otherwise.
I began to spread my influence, destroying gangs and taking their members until I owned everyone and everything. I would take Quirks with reckless abandon, but planned carefully. I even lent powerful Quirks to my agents, such as a teleporting Quirk to a man who took a fall for me so he could escape prison, then I would take it back and use a Quirk to change his features so he wouldn't get caught again, that is, until I owned every judge and jury.
But my brother did not see it as necessary measures to make us untouchable, but as me going mad with power, and in hindsight, he was right. By the time we were grown I was so desperate to get him to love and idolize me again that I forced him to take a powerful Quirk, and thus One For All was born.
He ran from me and joined a resistance movement against my power, only to die with them eventually. I mourned my brother, but then found out about his dormant Quirk. He had given his power to some child and it's power grew exponentially, with the boy obtaining triple the strength of my beloved brother. I was furious. That was the last thing that connected me to my brother and it was in the hands of some pitiful nobody? I became fixated on recovering my brother's Quirk at all costs, and chased the users to the ends of the Earth.
I spent so many years in control as I tried to take back One For All, and killed countless people in my attempts, until I killed one Nana Shimura, who was the seventh holder of your Quirk. She passed it to a young, Quirkless, little scrap of a thing who later would make his debut in America while I worked to control Japan.
While he was gone, I walked through my domain. I did this often, as all who had known my face were long dead, but this time I happened upon a woman who grabbed the last apple in a stall that I had my hand on. I used to have quite the build, and I towered over her, but she refused to budge.
'Um, Mister? Can you let go of the apple? I need it for a pie, but if you let me have it, I'll bring you a piece when it's done. Deal?' The woman asked with a bright, warm smile.
'Tch, I don't want pie. Take your fruit.' I spat, hoping to push this sunny person away, but only managing to make her smile brighter.
'If you say so, tough guy. I'm going to bring the whole thing back here, and if an anonymous stranger who gave me an apple was still here, I'm going to share it with them.' she said, turning and walking away, presumably to her home for her culinary activities.
I have no idea why I waited there, no idea why I felt the corners of my lips tug upwards when she waved to me, a picnic basket hanging off her other arm, and absolutely no idea why I went with her to a park to enjoy the food she prepared.
She asked my name, I gave it, my brother was the last person who could connect it to All For One anyway, she told me about her Quirk and asked me about mine, I lied and named one of the many Quirks I had stored, and we watched the sunset together.
I began to see more and more of the woman, going to movies and cafes and trying not to let her thaw my frozen heart, only to fail completely.
I proposed and married her, and that was the happiest I had been since Yoichi died. I lived happily with her and fathered my first born child. I knew that our child would most likely be Quirkless due to my genetic material being of a time when Quirks were uncommon, or their Quirk would take after their mother's, with a miniscule chance that it would take after mine.
It turned out to be the second one, I looked at my first son's Quirk when he was handed to me just after birth and he had a Quirk much like his mother's, that grew with his emotional state.
I took it from him, emotional based Quirks are dangerous during development, and gave it to his mother without her knowledge for safe keeping.
I lived with my beloved family until I was informed that the eighth user of my brother's Quirk had returned to Japan and wanted my head for what I did to his mentor. I told my wife that I would be gone for business for an indefinite amount of time, and that if it ran longer than expected I would remember to keep in touch, pat my son on the head, and left for battle. I lost.
I lost my empire, I lost my strength and longevity, and because of my disfigurement, I lost my family.
I was furious. I had found my peace and he came to take it away. My wife raised my son alone, and my son grew up Quirkless. I used my doctor to keep them healthy, sent them funds to provide for them and letters to talk with them, and watched them from afar as I pieced my body and my influence back together.
Everything changed when my wife was attacked. I still had a Quirk that stopped time, but it would only hasten my demise, so I hesitated, only for my son to charge in to defend her.
I saw myself reflected in my scrawny progeny and I was once again back in that fateful alleyway. He didn't have a prayer against the criminal but he fought anyway to protect his family. Instead of interfering directly, I did what I should have done long ago and gave my son a Quirk.
I now had a new reason to get One For All. My son would be able to use it like no one had before and would protect my wife when I was gone, so I continued my efforts when All Might eventually announced a successor, you, Young Midoriya.
Knowing where my brother's legacy was, I launched an attack to get it for my son, only to have my weapon destroyed and my forces to return with their tails between their legs at the thrashing they received from a mere teenager. That's when I learned your name, and changed my plans." All For One said, explaining his backstory to the young man who was cradling his girlfriend on his lap.
"Tell me your name." Izuku demanded his mind connecting dots.
"I already said, it isn't impo-" All For One said, only to be cut off.
"Tell me! Now!" Izuku said, his theory becoming solidified even more.
"My name is Hisashi Midoriya. I am your father, Izuku." The elder Midoriya said with a defeated sigh.
The uncomfortable silence stretched between them before Hisashi had a violent coughing fit, stronger than any before it.
"So- Izuku. I know you hate me, and you are right to, but my time draws near. Please, let me hold your hand in mine. Please indulge this as my final wish." The father said, stretching his hand to his son.
"I-I could never hate you. You were a monster, but you tried to change. I have every letter you ever sent me and every All Might figure you sent, even if you hated him. You never stopped being my dad just because you stopped being around." Izuku said in a broken voice, tears streaming out of his eyes as he placed his hand in his father's.
"Thank you, my son. Thank you. Even if I'm not quite gone yet, I think it is time you got your inheritance." AFO rasped, squeezing Izuku's hand with what strength he had left.
"W-What do you mean?" Izuku asked, not following what his father was saying.
"I just gave you my Quirk, son. You now have the power of both All For One, and One For All. I wish I had more to give you, but I know you will wield your power much better than I did." Hisashi said, his voice weak.
"I-I don't know what to say." Izuku said. "Do you want to say goodbye to Mom? I-I could get you to her."
"Heh, I want that more than you could imagine, but it's better this way. Let her remember the husband I was to her, not the man I was to the world." Hisashi said, his hand falling out of Izuku's as his arm grew weak. "You could do one thing for me, however."
"What? Tell me." Izuku said, picking his father's limp hand back up.
"I made quite the mess that I won't get to clean up. The computer over there has all of the information on the League of Villains. Stop them for me, Izuku. I have done great harm in my life, but please, help me to not be responsible for any more." He said, his voice barely a whisper as he quietly passed.
"I will, father. I will." Izuku sobbed, knowing his father was gone.