Kazuya you actually have a reason to kill Jin cause Jin has your other half devil and in Tekken 4 kazuya ending it showed that you wanted to take your other half from Jin but miserably failed and got your ass kicked
Actually. Not anymore. He's already unleashed his true devil powers to its fullest so in actuality, he doesn't even need his power no more especially since Heihachi is no more. Long story short, he considers Jin's devil gene obsolete now that he has unlocked the power of the devil gene to the fullest. If anything, he wants to reconcile with Jin now that he's fulfilled his goal of revenge.
You know when you ask me it makes a lot of sense kazuya would be relieved his mother and his father started the whole thing second his mother tried killing him she made kazuya have the devil jin in the first place so her dying would totally be a relief tp kazuya
Jin Kazama's Tekken 3 Ending (Canon): Jin Kazama has finally defeated Ogre & avenged his mom Jun Kazama's apparent death. However, Jin's victory was short-lived as he was gunned by the Tekken Force, even his grandpa Heihachi Mishima. As Heihachi walks away, Jin's Devil Gene was triggered as Jin took down the Tekken Force & even his grandpa. Jin flies away to Australia. Jin Kazama's Tekken 4 Ending (Canon): In his dream, Jin Kazama was haunted by the visions of his dad Kazuya Mishima & awaken to find himself in chains inside the Mishima Compound called Honmaru. Jin broke himself off the chains & fueled by the rage within the Devil Gene. Jin took down his dad Kazuya & even his grandpa Heihachi Mishima. As Jin prepares to deliver the final blow to Heihachi, Jin was stopped by the vision of his mom Jun Kazama. Jin spares Heihachi's life & wanted him to thank Jun for that. Jin sprouts his wings & flies away from Honmaru. Jin Kazama's Tekken 5 Ending (Canon): Jin Kazama has finally defeated his great-grandpa Jinpachi Mishima, founder of the Mishima Zaibatsu who lost everything to Jinpachi's son Heihachi Mishima, turns to dust. Jin became the new owner of the Mishima Zaibatsu which really puts a smile on his face.
So... now we all know the Mishima boys are all about killing each other, Chaolan...lucky b*tch. So.... All Kazama Jin endings...Hwoarang...you like redheads? *wink*