I dunno how I feel about mirio coming back...
of course, I love the guy! absolute favourite arc of any character I think I've seen in anime during season 4... but the reason it's so amazing is the fact that he loses his power. and how he takes that loss. how amazing of a person he is in spite of that loss.
This takes all that back. That loss isn't a thing anymore, so that arc isn't a thing. Every time I see that arc now its gonna be ruined by me knowing that it all gets turned back...
him in that room protecting that child is - or maybe was - an amazing scene, even more so in repeat viewings cause you know what's gonna happen. that's the part that always made me reaaally feel something in that fight... and now it's not there.
I'm gonna wait for an explanation, see how they handle that, hopefully, it's not just "we needed to practice her quirk, so we tried it on him first! and it worked great!", cause then the girl just lives up to what everyone (the fans saying shes just there to fill plot holes or however they worded it) worried she would be.
tl;dr: imo the explanation needs to be real good or it could ruin season 4's arc.