We only saw the Joker Buckle etched to Kenzaki, so we don't know if he has a Joker Form or not like Hajime or Shimura, because Kenzaki was forced into a Joker.
He sacrificed his humanity in order to save Hajime and in turn, the Battle Fight resulted in a stalemate. In the end, he is allowed to keep his Human Spirit card to maintain his disguise and stays with the Kurihara family for the rest of his life; but still remembers what Kenzaki has done for him for if he and Kenzaki cross paths, fate will step in and force them to fight again.
He sacrificed his humanity in order to save Hajime and in turn, the Battle Fight resulted in a stalemate. In the end, he is allowed to keep his Human Spirit card to maintain his disguise and stays with the Kurihara family for the rest of his life; but still remembers what Kenzaki has done for him for if he and Kenzaki cross paths, fate will step in and force them to fight again.