So I was shipping Jelsa before I even saw Frozen, and I felt like writing a story where Jack is sent into Arendelle to help Elsa learn how to control her powers. This is the first chapter. As of yet, I have no idea how long it's going to be, and I am basically making this entire thing up as I go along. The only thing I do know is that Jack Frost and Elsa WILL END UP TOGETHER =D
T-rated story.
Disclaimer: All characters belong to their respective makers. I take no credit for them.

WINTER'S HEART – By Lonely God
The Other World.

Jack Frost flicked off his hood as he walked into North's main meeting room. The others were all there already, and they all stopped talking to greet Jack, Tooth even jumping up to hug him and inspect his teeth. After he had taken his seat, North stood up to talk.
"Now that we're all here, it is time to begin."
North waved his hand, and a hologram of a citadel appeared in front of him, covered in snow.
"This is – Was – Arendell, a city in another world, another realm."
"What happened to it?" Jack asked.
"The new queen. Elsa was born with powers to control ice and snow, and on her coronation ceremony, accidently started an eternal winter. Fortunately for the people who live there, she and her sister, Princess Anna, were able to set everything right."
"So why does this have anything to do with us?" Bunnymund asked.
"Simple," North said, "Elsa still has her powers, but she has limited control over them. And our realms are linked. When things go wrong in either, it can bleed into the other."
Jack nodded. "I noticed that things were going a little out of whack recently. The snow was a bit more wild than usual, and I had nothing to do with it that time."
North continued on. "In short, we need to aid Queen Elsa in learning how to control her powers before any more problems occur. Jack, this means you."
Jack laughed. "I kinda figured that out from the whole ice and snow business."
North waved his hand again, and the hologram winked out. He then motioned for them all to follow him as he led them through his workshop. They made it to his sleigh, and he turned to look over them.
"Jack, you're with me. Everyone else, you can tag along, or you can leave."
The others all decided to head back to their respective jobs, after making North and Jack promise to keep them updated.

They quickly took off, flying higher and higher. North pressed a button on the front of his sleigh, and the sky burst into the colours of the Northern Lights. Jack smiled as he looked up at them.
"I always loved flying through them." He admitted to North, who laughed.
"Many do. It is a privilege of being the Guardian of Wonder that I can control them." As he said that, the lights began to dance around them. The colours mixed together, and created a tunnel shape. North guided his sleigh straight through the tunnel, the Lights pulsing as the sleigh passed. Suddenly, there was a flash of blinding light, and Jack covered his eyes. He could feel a difference in the wind, in the air. He opened his eyes, and looked around. Indeed, he could see the citadel from the hologram on the ground, the fjords and harbour busy with ships and people walking around everywhere. People looked up and talked excitedly at the sight of the descending sleigh.
"Jack, a landing strip over the fjords, if you please?" North requested.
Jack nodded, and flew out of the sleigh. He skimmed over the fjords, waving holding his staff out in front of him. A strip of the water instantly froze over, allowing North to land his sleigh. Jack noticed that people started chatting even more at that.

North climbed out his sleigh at the dock, where Jack was leaning against a wall. People whispered about them as they passed, and Jack heard the name "Elsa" several times. Soon they arrived at the citadel gates, and were granted leave to enter the main hall. As they walked in, North handed over his swords, and they were ushered into the hall. However, instead of Queen Elsa sitting on her throne, it was Princess Anna who was waiting for them. She sat on a smaller throne to the side, clearly bored with everything, although her eyes shot up to Jack's hair colour.
"Greetings, your highness." North declared, echoed by Jack. "We came to see your sister."
"About what?" Anna asked. "And what are your names?"
"You may call me North. And this here is Jack Frost."
"Frost, you said?" Anna asked, now hanging onto every word."
This time, Jack spoke up. "Yes, Highness. I am the Spirit of Winter in our world. I came because what happens here, can cause trouble for us. And I wish to help Queen Elsa control her powers."
Anna sadly shook her head. "I'm afraid that she can't keep it down. It's why she's not here today."
"I'm not saying I want to help her keep it down, I want to help her learn to use it properly so she can control it perfectly and doesn't cause another eternal winter. I saw that she has some control, and the Ice Citadel was well made, but from what I was shown, she doesn't have full control all the time yet."
Anna was obviously considering it. Soon she waved a servant over. "Give them rooms, and ensure they are fed. I will let Elsa know that they're here when she returns."
North interrupted. "No rooms for me, your Highness. I am not staying." He turned to Jack and handed the Winter Spirit a red and green whistle. "When you are ready to return, blow this and I will come and pick you up."

Well, that's it for Chapter 1. Will have the next one done soon.