A.N. I had actually written this story...I guess roughly around when flowerpower71 was first working on her Rise of the Guardian story I Believe. Back then I had originally named Jack's sister Pippa - since she hasn't been given an actual name yet - so flowerpower71 used that name for her as well when she cameoed in I Believe.
However around...last year I guess...flowerpower71 and I discussed her name further and decided to change it due to one of Jamie's friends being named Pippa (we wanted to avoid confusion). So after a while we decided on the name Rosanna, Anna for short (and Rosy for when Jack is annoyed with her or is teasing her). So in all of my stories and flowerpower71's future chapters/stories she will be named Rosanna even though she's still called Pippa in the early chapters of I Believe.

It was right after the guardians left at the end of the movie. It turns out they were heading back to their own homes, with North giving them a ride there. During the first leg of the ride...

"Um...Jack?" Bunny said awkwardly. "Sorry about...you know, losing my temper earlier. I was wrong when I said that we should've never trusted you."

Sandy looked shocked and then rose up and glared at Bunny while sand-steam came out of his ears. Bunny drew back, a little frightened.

"Easy Sandy, it's okay." Jack said.

Sandy looked surprised, but sat back down.

"Really?" Bunny said.

"Yeah, I mean losing Easter was a big blow on all of you so I don't blame any of you for getting upset about it." Jack shrugged.

"So...what were you doing at Pitch's place anyway?" Tooth asked.

"It wasn't intentional, I just... Well, after dropping Sophie off I heard a familiar voice and automatically followed it. The voice led me to Pitch's lair, so I realized that the voice was coming from my memories." Jack explained. "I was right, the voice belonged to my sister."

"Sister?" North repeated.

"Yeah, back when I was alive - in the 1700s - I had a family, including a sister." Jack nodded. "However I didn't find out then because Pitch was holding my memories, though he did toss them to me a little later on. He also tried to feed off my fear of never being seen and never finding out why, and tried to make me believe that you guys would never accept me. I got so mad at him that I started attacking him, but he ended up tricking me into leaving his lair and accidentally leave Baby Tooth behind. That was when I ended up in one of Bunny's tunnels, and realized that he was just distracting me so that I couldn't help you guys protect Easter. After I later left Britain Pitch showed up again. He tried to recruit me into helping him but I refused, so he tricked me into handing over my staff in exchange for Baby Tooth. He wouldn't let Baby Tooth go after all so she ended up having to jab him in the hand to be set free. Then Pitch broke my staff and sent me into a crevice. That was where I finally saw my memories and found out about my family. After that I fixed my staff and decided to free Tooth's other fairies, but they were unable to fly. That was how I found out about the last light: Jamie."

"Heh, bet your sister was a bit of a troublemaker like yourself." Bunny smirked.

"Not really, at least not what I saw of her." Jack smirked back before looking solemn. "But she was in trouble once...nearly fell through the ice of that pond where I normally hang out. I had to convince her to play a small round of hopscotch to get her to safety...though it was at the cost of my own life. Later that night I was brought back to life as Jack Frost."

Bunny gaped at him. North looked at Jack shocked for a moment but then looked at him proudly. Sandy too looked at Jack proudly. Tooth on the other hand already knew about that story so she just looked at him sympathetically.

"Hold on...you mean to tell me that you sacrificed your life for your sister? A kid?" Bunny double-checked.

"Well I didn't know whether I'd die saving her or not, but...yeah." Jack nodded.

"Crikey...no wonder Man-In-Moon picked you." Bunny had to admit.

"And with Jack's center being fun, and him having used fun to save sister..." North added, smiling.

"Yeah." Jack smiled a little. "That's exactly why I was chosen."

"You know your story sounds very familiar..." North muttered before snapping his fingers. "Aha! Now I remember: it was back during the 1700s, I heard about brother who sacrificed life for his sister in Burgess: Jackson Overland."

"Jackson...that name does sound familiar. What was his sister's name?" Jack asked.

"Rosanna." North replied.

"Rosanna...yeah, that also sounds familiar." Jack accepted that. "So I guess my full name is now Jackson Overland Frost."

"Is very likely." North smiled.

After that Bunny and Tooth were dropped off at their homes. Sandy left on his own after giving Jack a hug of gratitude for his help, since he didn't want to risk North's sleigh messing up his sandcastle home.

"So, now is time to take you home...or you could move in with me if you like." North offered.

"Really?" Jack smiled.

"Of course. We are both winter-type Guardians after all." North smiled back.

Jack thought it over.

"Thanks for the offer North, it really does mean a lot to me...but I'll have to decline." Jack decided. "My true home is in Burgess, where the kids are...and especially where Jamie is."

"You feel special connection to Jamie?" North guessed.

"Yeah...I mean he is my first ever believer...plus he was so brave against Pitch. Much like us Guardians really." Jack smiled.

"Is true...I wouldn't be surprised if he ever became future Guardian." North admitted. "But I have no say in such a thing...is entirely up to Manny."

"Well, if it ever does happen I hope it happens after Jamie has lived a much longer life than I did before I died." Jack said. "More like...well, you."

"You mean to old age?"

"Exactly."

"Me too."

North then dropped Jack back at the pond in Burgess. It turns out Jamie, Sophie, and their friends had become really tired after the long night they just had and were already gone. Jack didn't mind, despite not needing to sleep he kinda fancied a nap. It felt like a long time since he gave Jamie that epic sled ride after all.

Hours later Jack woke up, deciding that he should give the kids that were out a little fun outside to make up for most of the day having lacked his brand of fun. And among those kids was Jamie.

Jack had to note that he did feel a special connection to Jamie, just as North had guessed. Yes he cared about all kids, but Jamie...he was almost like a little brother to Jack. This made Jack wish even more that Jamie would one day become a Guardian after he lived a full life.