Let me explain apparently Izuku didn't have enough quirk factors in his DNA.
Which we both didn't find out yet but Today proves it because after a certain somebody told Him to swan dive off the roof. Deku stressed himself out enough to activate his Quirk which he got from he when we were little we fought for what reason well he thought his mom loved me more because he was still Quirkless. (Not true by the way) and in anger I bite him filling the gaps in his DNA but remained inactive leading to now. While Izuku lost in his Disparity. Waiting for him by the school entrance like aways he was takeing to long to talk with the teacher at least that what he told me. I focus senses to find him and heard his bones shifting. Running proximity to where my brother was I saw bakugo running scared I don't blame him the first time my bones shifted it was gross looking. Not expecting it to happen probably looked like a horror show. Finally I found Izuku still crying I crouched down and said "you ok bro what happened?" He dried his tears looking at me and said "I hate not having a Quirk it's not fair". Shocked he didn't realize I spoke "dude forget what others think about you and look at yourself do you seriously not notice you have fur now" i saw his face go blank. I started laughing "for someone so smart you sure don't pay attention enough fanboy" staring at his hands( well paws now) he screamed."Whaaaaaaaat"!