Harry and Sean prepared for battle the instant Voldemort finished his order. As Sean tightened his grip on his sword he quickly asked Harry "do you remember what I said about how to kill a vampire?"
"Run it through the heart with a sharp object" Harry answered.
"Aye, and the best way to kill an Inferi?" Sean asked.
"Decapitation" Harry replied.
"Aye, now get behind me and get ready to use your magic."
With that, Harry and Sean stood back to back. Sean put his sword in his left hand and then grabbed as many arrows as he could fit into his right hand out of his case.
"Move with me" Sean instructed Harry.
Harry had out his wand and the sword of Theseus, which was now glowing white hot and ready to be used for the first time in millennia. Voldemort's minions came at them, and what happened was disastrous for them. Voldemort had expected the sheer number of his forces to overwhelm any resistance, but now he was witnessing a Muggle and a 17 year-old wizard annihilating those forces.
Sean began firing arrows at an incredibly rapid pace and was moving so fast that Harry almost couldn't keep up with him. Sean would fire one arrow and then load and fire another and another and another until he had fired all that were in his hand. He would then grab another handful and repeat the process, with every single arrow hitting it's intended target.
Harry was glad that he had learned how to cast spells without uttering them, because there was no way that he would have been able to keep up with Sean otherwise. He emptied his mind and would cast a number of charms; he was able to instantly distinguish between a Death Eater and an Inferi. For the Death Eaters he used Stupefy, for the Inferi he used inflamare.
Harry and Sean kept this up until Sean announced that he had run out of arrows, but he was actually hording two in his case. At this, Sean closed up his crossbow, and drew his swords.
Harry kept his weapons out as he had them, and then Sean gave the instruction, "you take the left side and I'll take the right side."
With that, they began fighting their foes, Sean fought them hand-to-hand and with his swords, and Harry used a combination of hand-to-hand, the sword of Theseus, and magic.
Harry had only seen Sean fight in their spars, now that he was seeing how he did when he wasn't holding back…he saw that he was brilliant. Sean attacked with a combination of kicks, and attacks with his swords. He was incredibly fluid in his movements and precise in his attacks. He would destroy Inferi with a combination of foot sweeps sword thrusts and devastating kicks. Death Eaters couldn't hit him with their spells, and after he would dodge one, he would avoid the spell, which was almost always the avada kedavra, and then sprint ahead to kill the Death Eater that tried to get him.
Harry was equally impressive and using kicks, the magic sword, and his wand magic to destroy the enemies that were befalling Sean and himself. He had mastered performing charms without having to say them, and the Death Eaters having to say their charms gave him all the advantage he needed. Harry would not use any of the unforgivable curses; he was determined to defeat Voldemort and his forces without sinking to their level.
Voldemort had sent all of his Death Eaters with the exception of the Malfoys into the fight, leaving no one but them to guard the faculty, himself, and Scrimgeour. None of the faculty though could take their eyes off of the display in front of them. They all knew Harry, and now they were seeing him fight like he was, they watched him and his companion take down foe after foe. Inside they were theorizing as to what his companion was, no one thought that it could be a Muggle, he was doing things no wizard had ever done before.
After the battle had waged for a few minutes, Hermione and Ginny saw their chance. Hermione nodded to Ginny who ran for the door as Hermione pointed her wand to her throat and amplified her voice.
"All students, head for the door immediately, move as fast as you can in an orderly manner" Hermione began, "your prefects will escort you to your common rooms."
While she spoke, Voldemort took notice, but figuring that the students weren't leaving anyway, told his forces to ignore them and kill the spare and restrain Potter. The students proceeded out of the room in an orderly but still somewhat hysterical fashion. The last ones out didn't even bother to close the doors before making their way to the main hallway and following the other students to the great staircase.
After about twenty minutes of fighting, Sean thrust the sword in his right hand through the heart of a vampire and then with his other sword took the head of the last of Voldemort's minions.
"That's im-pos-sible" Voldemort muttered to himself in a tone that reflected his and Scrimgeour's utter disbelief at what had happened.
There were bodies all around the two young warriors who stood emotionless over their kills. Many Inferi lay on the ground headless, many vampires lay on their backs or fronts with blood gushing out of their chests or where their heads used to be, and many Death Eaters lay dead from Harry's spells or sword, as well as Sean's arrows or swords.
Harry stared down Voldemort while Sean stared down Scrimgeour, all the while holding his bloodstained swords in his hands.
"Luscious," Voldemort said in his usual sinister voice, "take our guests to the dungeon, I will deal with these pathetic fools myself."
"Like hell you will!" Harry shouted angrily. "You will fight me and me only…it ends here and now!"
Scrimgeour walked to the side of Voldemort, "I will kill the spare, Lord Voldemort."
The four enemies looked each other over and none of them wavered, a standoff ensued with Harry and Sean's eyes meeting those of the men challenging them.
"This is between us," Sean said to Voldemort and Scrimgeour. "Let them go" Sean said pointing to the faculty members with the sword in his left hand while he sheathed the one in his right.
"And why should we do that" Scrimgeour asked.
"There's no one to guard them and you will be fighting us" Sean said simply.
Luscious Malfoy spoke at this point, "why you…gaahaugh" he was stopped by one of Sean's arrows through his throat as he fired a second into Draco's chest, killing them both instantly and using the last of his arrows.
The two Malfoys dropped to the ground dead as the horrified faculty looked on. Scrimgeour looked at Sean who had closed his crossbow and sheathed his sword.
"I see that we are at an impasse," Scrimgeour stated.
"Not relatively" Sean said as he turned to McGonagall, "leave us!" he said to them.
McGonagall stood up slowly and then began leading the faculty out, Voldemort and Scrimgeour paid them no mind as they were staring at their enemies.
They continued their stare down until Sean broke the silence. "The Order of the Phoenix and a few Knights of the Order of St. George will be destroying your werewolves and Dementors momentarily, if not now." A slight smirk came to his lips as he continued, "Hopefully Bill will use my wedding gift."
"Face it Riddle" Harry began to Voldemort, "you've been backed into a corner."
Voldemort realized that he was in a tight spot, he decided the only way to win was to destroy Harry.
"Very well then Potter" Voldemort spat out to Harry, "we will settle this once and for all. And after I have killed you, I'll put your body on display in the Great Hall."
"And after I kill you Riddle" Harry replied with ice in his tone, "I will burn your body and scatter the ashes so that there will be absolutely nothing left of you."
The four duelists faced each other with aggressive looks and prepared for what would be two final showdowns between mortal enemies, Harry Potter and Tom Riddle, and Sean O'Sullivan and Rufus Scrimgeour.