This chapter, named King of Fist Raoh (拳王ラオウ) is comprised only of the boss fight against Raoh (or Wang in Black Belt). Raoh's attacks are much stronger than yours, but as long as you dodge appropriately, this shouldn't pose a problem. Sometimes, Raoh will jump; wait for his descent to punch him down. Most often, Raoh will perform a punch or kick with great reach. Counter this with a jumping kick, avoiding the range of his attack completely and simultaneously pushing him away. As long as you properly utilize jumping kicks and attack him as he descends from his jumps, this battle should go the same way as all others, resulting in victory for Kenshiro or Riki. When Raoh/Wang is on his last bit of health, make sure to finish him off with a standard punch, as this is the only way to clear the fight.
After the fight, Raoh will die with his fist to the sky, and Kenshiro will finally be reunited with Yuria (or Riki with Kyoko). Congratulations! But this isn't the final challenge the game has to offer you. Once the couple is reunited and the final message is displayed, press 
twenty times to enter Chapter 7, which serves as a boss gauntlet. Your health does not restore at any point in this gauntlet, making it the ultimate test of skill.