>>279676802Toya was born with her condition so he gave up on him when Shoto was born.
Despite this Toya kept training because he wanted to make Daddy proud.
When Endeavor found out Toya was giving himself permanent body damage from overtraining, he slapped her for not stopping him.
What sells the scene is that she says she couldn't stop him on her own.
Later on "Toya's death" combined with Endeavor pushing Shoto in the same direction must have given her PTSD which leads into her burning Shoto's face.