DISCLAIMER: I don't own Superman or Star Wars.
Superman flew across the sky, leaving a red streak behind him. Suddenly, he heard someone calling for help. He flew down to the ground, landing between a man with a suitcase and another man, who wielded a red laser sword. The man with the suitcase ran away, while the man with the laser sword stepped forward to face Superman. "That's enough! Throw aside that weapon before you get hurt!"
The man smirked. "You are nothing to me. The Dark Side will take you!"
Superman flew forward, and the man swung his laser sword at him. Superman blocked the laser sword with his arm, feeling a slightly painful burn from it, but nothing serious. The man widened his eyes in disbelief, before releasing a blast of pressure, which blew Superman back, but otherwise had no effect. The man started firing lightning at Superman, but the lightning had minimal effect, merely singing Superman. Superman activated his heat vision, burning the man's shoulder. The man fell back, but recovered rapidly, charging with his laser sword. Superman blocked every attack the man sent his way, before charging forward, throwing the man to the ground. Suddenly, a voice called out, "Superman! I saw the explosion. What's happened here? Are you ok?"
Superman turned to see Wonder Woman floating above him. "Just fine, Wonder Woman. This guy's not too dangerous."
The man charged at Superman, swinging his laser sword, but Superman slammed him in the chest, throwing him to the ground.
"That's it. You have two options. You can give me that weapon and return with me to the Watchtower, or I can take the weapon from you and drag you to the Watchtower. I leave the choice to you."
The man smirked, placing his hand on his forehead. "Wonder Woman is your enemy."
Superman felt the man attempting to take control of his mind, but he was easily able to resist it. Starkiller's mind was suddenly filled with Superman's voice. "And I look silly in tights. I know. Mind tricks have no effect on me."
Starkiller, his mind control worthless, was suddenly overcome with a terrible headache.
Superman took the lightsaber from Starkiller's weakened grip, grabbing him by the shoulder.
"That's your own power that gave you that headache, you know. I didn't do it. Now, I think I know exactly where to take you."
Starkiller struggled to attack with his power, but Superman easily held him in place.
Starkiller gasped, "I cannot fail my master!"
Superman struck Starkiller in the side of the head, stunning him. "We'll eventually see about this "master" of yours. From the sounds of it, I think you could do better."
Batman looked at the unconscious, twitching Starkiller. "He seems slightly unstable. You have no idea who he is?"
Superman shook his head. "He isn't in charge, wherever he comes from. He was sent to do this by some kind of "master". He may be evil now, but I think we may actually be able to save him."
Batman stepped out of the room. "I hope you're right, Clark. This guy couldn't beat you, but he's still very powerful. I don't like the idea of him fighting the rest of us while Doomsday or Darkseid keeps you busy."
Message to readers: As powerful as Starkiller is, he simply doesn't compare to Superman's power. Here are some reasons why he can't win.
1. The Force is specified by Obi-Wan as being "an energy field created by all living things", and therefore is not magic. Therefore, Superman's invulnerability applies completely.
2. Lightsabers are laser devices, which also doesn't have much effect on Superman.
3. Starkiller can be defeated by normal means, as he is just a human in the end.