Is there a sign before his blades come out? Not really, they are pretty sudden
Is there a limit to how many blades he can produce? No there is not.
How far can they extend?, I'd say around 6 to 7 feet at max
Is there a specific angle which the blades extend - vertical, horizontal(?)? They can appear at any angle.
From almost anywhere - where are the places he can't extend his blades from? (um...that get's a bit awkward) but he can't usually spawn them by his stomach...or just a bit lower than that XD
How long can he manipulate someone? only for a few moments, or say 2 to 3 seconds at max
Does the manipulation fade over time? no it just suddenly stops
What do you mean by rip out of his flesh? he literally rips his body in half and the new form emerges from his old one
Do you mean he leaves behind a husk of his human self? yes he does
Or does he turn into a wyvern? no
Is he capable of ripping more than one dimensional hole at the same time? well, he could...but...he would probably hurt himself by doing so.
If so, how many? maybe 4 or 5 before collapsing
More power? As in strength am I right? you are correct
Wait, does that mean the blades come from beneath his skin? they do, they go in between his muscle structure so he doesn't cut through anything important
So you're saying that Kai gets hurt when he produces these blades. he does hurt himself, but remember that he can heal if left alone
Wouldn't that mean that if he used too many blades there would be too much blood loss resulting in collapse? if he makes to many at one time he would
How strong is this guy exactly? decently strong in upper body, but he is RIPPED BEYOND COMPARE in his lower body
He damn sure has a lot of leg muscles for that amazing leap(I've noted the fact that you said intense lower body strength). To blow the pavement into pieces is not an easy feat I'm sure. yeah, that is partially from him punching it with his feet and partially from gravity (he likes to use his knowledge of other forces such as gravity and friction)
So at first, it seems like Kai is going to help this woman get her purse back and be nice. He says thieves think they can get away with doing bad right? So that should make him the good guy in this demo. If you note he said "why do all the OTHER guys think they can get away with this" this would imply that he was a thief himself.
Firstly - ouch. I thought Kai was going to be nice and give the woman back her purse. Did he change his mind all of a sudden and decided, "hey you know what? I'm going to kill this lady and take the money instead."? no his intention was always to have the purse, i wanted you all to think that he was going to be nice
Secondly, do you mean shot as in he released a piece of steel from his body and shot it into her or stabbed her? he ejected it, and yeah definitely ouch!
I loved answering these great questions, and thank you for adding me to the hitlist. Do you think you can battle me soon Rage?

Yea I can battle you whenever you want. I'm pretty free during the last weeks of December. Better grab me when I'm available.
EDIT:

very perceptive, he would take damage from the blades when he transforms, and the blades would be permanent until he transforms back. Theoretically he can produce as many blades as he wants, but he does hurt himself.