This isn't my best work by far, but it's an idea that's been bouncing around in my head for awhile and I wanted to publish it. So here we go...
John, Master Chief Petty Officer, codename Sierra 117, had just lost his whole life. The earth, all of the Forerunner Halos he knew of, and even all of the new SPARTANs that were created, had been annihilated. He was now on this strange planet that looked Forerunner, but couldn't have been. The Forerunners were gone. He hadn't left his Pelican yet, because it had crashed atop an extremely tall building. He wasn't sure whether he would fall, or whether he would survive it. He very suddenly made a decision and kicked the rear door completely off the Pelican, which was easy with his enhanced strength from physical augmentation and armor. He stepped back, however, when he realized that the tail end of his Pelican was hanging off the side of the building. He shrugged and moved to the front of the dropship, ripping the front window from the ship. Before he left, he made his way back into the rear compartment and approached a weapon rack. He could never decide between the simple MA5B Assault Rifle and the Designated Marksman Rifle, or DMR. The Assault Rifle was a simple weapon. It was an air-cooled, gas-operated, bullpup fully automatic rifle, with a box magazine that held 32 bullets, and a bullet counter/compass display on the top of the weapon. The DMR was a precision weapon, also bullpup, with a 15-round box magazine and a 3x zoom scope. The DMR was very accurate at long ranges, naturally even more so at short ranges. Master Chief finally decided and picked up the DMR. He loaded up on more ammunition than he usually did, taking ten spare magazines instead of just four. What with the Energy Sword magneted to his right thigh, which didn't take ammunition, he had a lot of spare room. He made his way back to the front and jumped out of the Pelican.
Mace Windu raised his violet lightsaber. Anakin, to his right, shouted, and he had the urge to lower the blade. Anakin's own blue lightsaber slammed into Mace's, and the Emperor used the Force to throw Mace out the window into the night sky. Mace could see nothing but the stars, hear nothing but the destruction of the Jedi Order, think about nothing but watching his friend Ki-Adi-Mundi die. Until he sensed the building. He couldn't use the Force on himself, so he flung his lightsaber under himself with the Force and push it upward. His fall was slowed, and he snatched his lightsaber out of the air and landed lightly atop a large building. In front of him, he could see the dim shape of a squatting Clone Trooper in front of a crashed dropship. He heard a faint muttering: "How am I supposed to get DOWN from here? Cortana might've been able to help." Mace cocked his head, then grew angry.
"Stand up, Clone!" And the Clone did just that. Extremely quickly. With blaster raised.
"What?" The Clone challenged in a deep, battle-worn voice.
"I said, STAND UP! You have assisted in the destruction of the Jedi Order, and you are now to pay!" Mace activated his lightsaber, and it bathed the top of the building in a faint pink light.
And he realized his mistake.
"I'm no clone," the Master Chief said, "but I am responsible for a lot of destruction." Mace laughed at the man. He was wearing durasteel armor, but it was bulky, and therefore heavy, and had a glass facemask. It would be easy to cut through that. As for his blaster, it was bulky and so outdated that Mace didn't even recognize it. Suddenly, the end of his blaster lit up yellow, but no blaster bolt emerged. Instead, it seemed something solid instantly punctured his shoulder. The Chief fired his DMR again, but this time the bullet was stopped in mid-air as Mace extended his hand. Four more shots, but each stopped before it found its mark. The Chief stopped shooting, and the five bullets dropped. Mace lowered his hand and tried to Force Push the Master Chief from the building, but John had seen him stop the bullets, and had a good idea what he was trying to do. The chief activated his rear thrusters, and grabbed a wing of the pelican. The two forces more than made up for the Force Push, and the Chief actually moved forward quite a bit. Mace was surprised, but started forward, raising his lightsaber. The Master Chief pulled the Energy Sword from his thigh and activated it. Mace swung his lightsaber, and John trapped the lightsaber between the two blades of the energy sword. Mace found that he couldn't move the lightsaber anymore, and lost his grip when John twisted the Energy Sword. He kicked Mace, who landed on the next building over. It was of no consequence, though. There was a thruster on the back of the energy sword, and it would drag the Master Chief forward with it in a lunging motion. But he took it three steps further. He stepped to the edge of the building, grabbed an antenna of some sort, and bent his knees. He activated not only the energy sword thruster, but his armor's thrusters, he lunged forward with his legs, and pulled himself forward with the antenna. Within a second, he slammed into Mace Windu at upwards of 150 miles per hour. The Energy Sword passed clean through the Jedi, and the battery died. Mace wasn't dead yet, though would be in a few seconds. Master Chief pulled the dead sword handle away, and realized it was a fistload. Not only that, but his armor enhanced his strength, and his physical augmentation. With that knowledge, he punched Mace Windu in the face with all of his might, and completely shattered the front of his skull and destroyed his brain, sending him flying from the building. He never had a chance of survival.