After the events of Turtles Forever, Karai decides to give up on the whole "getting revenge for The Shredder's demise" thing. After all, last time he fought the turtles he nearly destroyed the entire multiverse, including himself and Karai. Therefore, she finally decides to leave the turtles alone and not to look for a way to bring The Shredder back. However, Hun (who was cured of his previous mutation by Donatello, who injected a curing medicine into him after the turtles knocked Hun out in a fight) disagrees. One night, Hun pays a little visit to Foot Headquarters.
Hun: "You know, Karai I've been thinking. When I first found out Shredder was an Utrom, I thought "Good riddance". But after working for him once again, I had suddenly remembered what a thrill it gave me to serve someone so powerful and full of vengeance, Utrom or not. So the Purple Dragons and I have come up with a great idea: "join forces with you, the Foot once again". And together, we can bring him back, the one, true Shredder! Are you interested?"
Karai: "I am pleased with your offer, Hun. However, I'm afraid I must decline. After The Shredder and I last tangled with the turtles, I realized that although he raised me he was a very stubborn, power hungry being. He was going to do anything he could to destroy the turtles, even if it meant mine and even his own doom. He was indeed my master and father, but he was also a monster. I've decided to turn over a new leaf and start a new dynasty with the Foot. I'm sorry, Hun but I can't help you."
Hun: "Fine. Those who are not with me are against me! I'm taking over the Foot, just try and stop me!"
Then a fight breaks out between the two. 2003 versions only (although I'm not sure there are any other versions of Hun). Rules are simple: one-on-one (no interference from anybody) and Karai only fights with her own signature equipment, no Shredder armor or weapons like she did in Seasons 4 and 5.