Chapter 4:
With everyone watching intently Souma and the King walk onto the battlefield and meet each other at the halfway mark in the arena. They bow in front of each other and get in positions to start the fight. Souma, unsure of who will make the first move, decides to go full on Asta mode and dive in head first towards the king. The King who was able to anticipate his recklessness, prepares to intercept Souma with a magic induced punch which immediately connects with Souma's stomach which causes him to cough up blood.
Souma thinks to himself "Awwwww Holy Shit that hurts, how am I supposed combat that even with Itadori's immense battle and martial arts knowledge and strength, this guy's a whole different type of demon, it's as if Toji Fushiguro, Rimuru Tempest, and a fucking cinder block suddenly combined as one and is now coming straight at me with nothing but malicious intent. I can only think of one thing that would even scratch him but I can't remember how in the hell I'm supposed to activate Hollow Purple. So for now I'm gonna fight to the best of my ability and hope I can activate a recurring Black Flash like Yuji did to Sukuna and Mahito. Guess I'll rely on the time delay attacks and blood manipulation till I can remember the activation sequence for purple."
Souma then standing after taking such a dangerous hit dodges the King's next attack and starts to go on the offense connecting a punch to the king's stomach which causes the king to go flying at least five feet with the delay of the punch. The King suddenly comes to a realization that this kid's power is something other than magic. With this realization the King prepares to use more force in his attacks for him to fully understand Souma's abilities.
But as he is preparing his attack, Souma launches a piercing blood directly towards the King which connects and manages to actually pierce the King's skin. The king, completely caught off guard by an attack he's never seen before, begins to realize that Souma is a battle bred machine that when fully nurtured he must not take his eyes off of him or else he may very well die. But that does not matter as the King has prepared his attack and amplifies it to the max and sends it directly towards Souma.
Souma, unable to dodge, ends up taking the attack directly to his body but in that split second he uses reverse curse technique so he's able to survive much to the King's and all of the spectators' surprise.
The King, completely dumbfounded, asks Souma "How are you even alive and able to still stand up." Souma replies "Because of the reverse curse technique."
The King asks what the reverse curse technique is. And Souma says "When you threw that attack at me, I gave up on counter attacking and poured all my focus into the reversed cursed technique." The Demon King asks "What is this so-called cursed energy and reverse curse technique you speak of?"
Souma replies "Cursed energy is negative energy. While it can enhance the body, it can't regenerate it. So you multiply that negative energy against itself to create positive energy. That's the reversed cursed technique!"
Everyone watching is confused but the King has a grasp of what's happened and decides that pure hand to hand combat might be best in this situation.
And Souma suddenly remembers the activation sequence for purple watches when the king comes at him with all his force. The attack connects and it seems like the King has won everyone has started cheering but Souma begins to float up and Everyone one looks in disarray as the King seems to pull the finishing blow Souma than says "Nine Ropes", "Polarized light", "Crow and declaration", "Between front and back", "Imaginary technique, Hollow Purple".
And sends it towards the king in full force. And it hit the King and he couldn't put a shield up fast enough so he just takes it and fell to the ground. Realizing he's gonna die if he tries to keep fighting, So he says out loud "I yield".
Everyone stares at the fallen king with shock and fear of what they just saw and then at Souma who's barely able to stand. So Lucille declares Souma the winner.