Sad Excuse

An Illness? Is it really just an illness? Or one that was given at birth, and lead to a devastating future?

Izuku was born with an Illness. This illness will slowly take his sight, then his hearing, it will even weaken his heart and lungs.
Izuku will soon wear a collar around his neck, but, not just any collar, a mechanic one, it registers his heart rate. If his heart rate increases some the light will turn yellow, if he starts to have a panic attack the light will turn red. If it's fatal the light will blink. Then you have the good green. That lets everyone know he's ok.
Now here's an interesting thing about Izuku, despite his illness, he does indeed have a quirk, but what may this quirk be.

Izuku's childhood was traumatizing. But, he has Katsuki to help him with the bullies.
Katsuki is still a little dickhead but that's ok. Because he tries everything in his power to help Izuku.
But will his help be enough?

Izuku is a traumatized child, and teen.
He hates crowded areas, he doesn't like the dark, and he doesn't like loud noises.
The only sad thing was, His mother, Inko Midoriya, was not the best mother. She saw her son as a needy, attention wanting brat.

Mature