Tekken 8's story mode has two endings.
According to the game's director and producer, Katsuhiro Harada, many players don't know this and are yet to unlock the second ending of the game which some have dubbed as the 'bad' ending.
This is an ending that seen Jin lose the final fight to Kazuya who then proceeds to throw his son's body from a cliff like he did with Heihachi many years ago in revenge.
Whether Jin dies in this scenario is unknown and it is unclear which of the endings is canon.
The regular ending sees Jin win the fight and Kazuya laying motionless. Jun walks up to him and in a mid-credit scene, we see Reina revealed as Heihachi's daughter and a wielder of the devil gene.
In a tweet, Harada revealed that the darker ending has been in the works since the late 90s when he first pitched it to his boss. And now, well over two decades later, we now see the fruition of that dream.