Izuku Midoriya died by the hands of his step-sister Izumi, the daughter of Inko Yagi(Magnet) , formerly Midoriya, she cheated on Izuku dad Hisashi Midoriya(Wyvern) with Toshinori Yagi(All Might) and Izumi was born at the same time with Izuku.
Izuku never knew that Toshinori was his step-father, not biological father.
At the age of 4, he was diagnosed as Quirkless. His mother, step-father, his step-sister and his friends(1A) change after that.
Inko and Toshinori started to neglected and abuse him.
Izumi and her friends started to bully, torment and beat him.
At the age of 14 he died by their hands.
Izuku mindscape
Izuku:So, I'm dead?
... :Yes. I'm sorry.
Izuku turned around and he see a dark figure with a scythe.
That person was The Grim Reaper.
Grim Reaper:You died before you'r therms, Young Izuku Midoriya.
Izuku couldn't understand why he called him Midoriya.
Grim Reaper:I think you may wonder why wonder why I called you Midoriya. But it's not up to me. Hisashi, you can come.
Another figure come. He had black curly hair and eyes like Izuku.
Hisashi:Son?
Izuku:Who are you?
Hisashi:I'm Hisashi Midoriya. You'r biological father. And I know that you're angry, but let me explain.
And The Grim Reaper come and put his skeleton palm on Hisashi head and showed his memory. How Inko cheated on him and how finding out about the hiding pregnancy test that was positive. How he died before he see Izuku by the building that crush him after he save the civilians.
Hisashi:I'm sorry, Son.
Izuku warped his arms around Hisashi, hugging him tight.
Izuku(crying) :It's okay, Dad. It wasn't you'r fault.