The Cave of Lucifer

The cave

It was a calm day in London, England, and the twins, Nexus and Nexia, were just sitting in their office waiting for an expedition order. Eventually, an email popped up on Nexus' screen that read, "I have recently come into ownership of a big chunk of land and was hoping you would be able to take a look at the land to see if anything is out of place." So the twins excitedly grabbed their gear and hopped in their truck to head out and see what they could find.
When they got to the property, there was an older man leaning against a tree. When the man saw the truck pull up, he gave a wave to the twins and walked over.
"Howdy," the man said enthusiastically, "you two must be the explorers I hired. The name's Kane, and I was given this property by my father, Lucifer, who figured it was time to pass it on. The thing I need you to investigate is a cave on the other side of the property that I recently discovered. my father says he never noticed it and said I should shoot you an email."
"Well sure," stated Nexus, "Nexia and I are always up for an adventure."
And so they hopped in their truck to get across the property much quicker, as it was about three acres of land.
As soon as they saw the entrance to the cave, they were instantly excited. The entrance had huge stalagmites and stalactites on the ceiling and floor and what appeared to be glistening crimson liquid dripping down the sides of the walls. Wanting to poke her head inside, Nexia attempted to put her hand on the wall but immediately pulled it away as the wall was scorching hot and sharp. She looked at her hand and noticed it was bleeding. Her blood dripped down the wall and as soon as it reached a weird circular crack, the entire cave lit up with lanterns all the way through the cave. Intrigued by the phenomenon, the twins walked in, but as soon as they did, the entrance crashed behind them. Right before the entrance was completely covered, Nexus saw Kane standing on the other side, creepily smiling at the two of them, but this time Kane had giant demonic wing protruding from his back. Luckily Nexia hadn't seen the same thing he had.
"Come on. Let's see where this tunnel leads," Nexus said, really wanting to get away from where he had seen Kane.
They started walking and rounded a corner before they came to fork, one path to the left and one to the right. They decided to travel to the right as their parents had always told them to go right if they ever found themselves in a maze or crossroad. They continued until they came across what looked like a really rough staircase leading downward. At the bottom, they could vaguely make out what looked like the shadow of a man, but there was something wrong about it. The shadow looked as if it had eyes and was blinking. The twins continued, but very cautiously and as they reached the bottom of the staircase, they realized the shadow wasn't a shadow at all, but an actual figure that was just staring at them and seeing if they were a threat. When they got close enough, the figure morphed into the shadow of a cat and started hissing like crazy. Not scared however, the twins continued forward and rounded the corner ant the bottom of the stairs into a huge round room with a fireplace burning purple and a cauldron that contained a boiling, milky white substance that looked like swiss cheese without the holes.
"AH!" exclaimed a low gravelly voice behind them, "You've finally arrived."
Nexus and Nexia turned around to see a man with crimson skin and razor-sharp horns protruding from his head with a flaming crown perched on top of his frost white hair. His outfit looked like a wetsuit, but had spikes around the collar, and he had a cape wrapped around his shoulders.
"And who are you?" questioned Nexus.
"Ahh of course. Your memories were wiped before you left," stated the man, "my name is Lucifer and I am the father of Kane who you bet up above, but I am also your father."
"That's impossible," stated Nexia, "our father died when we were little."
"No I didn't," said Lucifer rather sadly, "I faked my death. There was nothing else I could do. I was being called home and that meant I needed it to appear that I passed away."
"What do you mean when you say 'called home'?" Nexus questioned.
"As you have probably figured by my form, I am a demon," explained Lucifer, "I originate from the underworld, which in turn makes you half-demon as you were born of a human mother."
"Did Mom know who you really were?" asked Nexia.
"No, no one knew," Lucifer said, now crying what looked like liquid fire, "No one could know or the the human world would declare that the demon world had sent a spy."
"So why did you summon us here?" asked Nexia, still confused by all this.
"Simple, I wish to introduce you to the world that you could never experience, the power you never felt," stated Lucifer, still crying, "what do you say?"
"Of course we'll accept," said Nexus excitedly, "we're alway looking for new, exciting experiences."
Lucifer smiled, "great! I was hoping you would accept, Now in order to get through the portal, you must consume a glass of the liquid in the cauldron, as it will allow the portal to recognize your demon blood.
Suddenly, two chalices appeared in front of the twins and they grabbed them out of the air. They ladled the liquid into the chalices and drank. Immediately the twins felt their blood boiling and felt two wings grow out of their backs and rip their shirts.
"THIS IS INCREDIBLE!" exclaimed Nexus, "I FEEL SO POWERFUL!!"
"Good," stated Lucifer, "I was wondering how your bodies would react to the potion."
Lucifer raised a hand to the wall and said something in an unknown language, and a portal appeared where a weirdly shaped circle was etched. 
"Now when you step through this gate, you will feel a tingly feeling," explained Lucifer, "this is just the portal activating the rest of your demon blood that might have remained dormant when you drank the potion."
With that, the twins stepped through the portal.