Because of you, I will always have a friend

(Spoilers for Tomura Shigaraki's past.)
When Tomura Shigaraki or Tenko Shimura was only four years old, he was punished by his father for looking at a picture of his grandmother who was Nana Shimura. A hero. Tenko was forced to stay outside, during this, his decay quirk activated. Killing his whole family in the process.
This is what happens in the canon story of My hero Academia. But in Dusty Deaths, Tenko has an adopted brother; Izuku Midoriya. What happens when Izuku gets a quirk? A death quirk to be more exact. If any biotic organism comes into contact with Izuku's skin, they die instantly.
How does the story change?