Firstly in the history Mikado's first ever use of his semblance forcing back a Grimm which would overpower a full blown hunter even if said hunter is injured at ten years old is a bit much. I know what you are trying to get at but if you want Mikado to contribute to the fight have it slow the Crimera-Grimm down for Jack to finish off.
Awww rabbit sized dragon sounds so cute. I'm going to need you to specify that no one can ride the dragon tho. Just so everything is clear.
Combat behaviour could use some more detail as well, like how does Kiro fight beyond simply being most defensive. Should add more weaknesses as well, the pain link balances the semblance but not the rest of his combat behaviour.
Weapon is good but are there any dust functions?
I'd also recommend running this through grammarly or another grammar checking software to help with some of your tenses which got mixed up.
Most of your descriptions are fine but I'm going to have to come back to the Chimera-Grimm thing. You can have it live it's just having Mikado play a serious role in defeating it the first time as an untrained child isn't something we are OK with. Have it help Jack beat back the Grimm but it escapes or something like that.
Creation Powers. You cannot create a hammer made out of a physical matter. You can create a hammer made out of Aura, which would dissipate when you let go of it or ran out of Aura.
- Aura Constructs do not have consciousness, and cannot make decisions on their own. They will follow instructions given to them by their creator, however.
Now to his fighting style and other information, but befor this, it need to be said that Kiro is only a 'thing' created by auro. He is just an empty shell which can't do anything without someone telling him to, and this someone is Mikado and Mikaodo only.