Doesn't sound too complicated.

Basically, how it would work:
Make a message that says "FINISH HIM"
Make Uke's body go limp
Apply constant upward force on a couple body parts so Uke doesn't just fall
For the instagib thing, do something like what NewbLuck did with punchout - if Tori's fist is close enough to Uke's body, it decaps (you can put more into it - like checking with all of Tori's body parts, not just Uke's, making a minimum speed requirement, making Uke explode, not just decap, etc.)