Brother
Kristoff understood parents, he understood siblings, and he understood these are things he never had and would never have. He understood the cold and the ice and the wilderness in a way he would never understand family, at least not in the sense of someone who knew their family, their real family. Sometimes he imagined his father was a king and he was stolen away at birth by an evil witch, or that his parents died heroically fighting off enemy invaders of Arendelle.
He understood that he was a subject of the kingdom of Arendelle. He'd been told by people he sold ice to from a young age that he lived in a kingdom called Arendelle and that by virtue he was unwavering loyal to the king and would one day be unwavering loyal to his daughter the queen-to-be.
Kristoff understood brother from the very beginning though.
Kristoff had been six years old when he first found Sven, huddled alone against a tree stump in the snow.
"A moose?" he approached the animal. No, it was a baby reindeer, separated from its herd. "Hey little guy, I'm a little guy too."
The reindeer responded only in minuscule amounts to Kristoff's voice as he tried to approach him as slowly as possible but the crunching of snow beneath his feet made a stealthy approach impossible and the reindeer grew restless.
"I just want to say hi," Kristoff said. The reindeer struggled to get to its feet and Kristoff stopped.
He dug through his bag and produced a carrot. As far as his arm could stretch he reached out with the carrot, offering it to the reindeer. And the reindeer for his part had become intrigued, he made no move to come closer to Kristoff but he stopped struggling to get as far away as possible.
"Yeah, you like carrots huh?"
As if understanding him, the reindeer made a move to slide a bit closer to Kristoff. He stayed still like a block of ice. The reindeer scuttled closer, now only staring at the carrot, his thoughts clearly devoid of Kristoff. With shaky limbs the reindeer reached the carrot and bit down tightly, pulling the food from Kristoff's hand and beginning to chomp down on it.
"You must be really hungry, I have more," Kristoff offered a few more carrots. The reindeer bounced between them eating as quickly as possible. "You know, I could feed you more carrots. I could be the person who feeds you carrots."
Only after the last carrot disappeared did the reindeer look at Kristoff, this time with curiosity and wide eyes. Kristoff raised his hand and the reindeer's eyes followed it closely. He let his hand hang in the air, waiting for the reindeer to meet him halfway.
"It might be nice finding food for someone else too, it's probably what family feels like."
The reindeer moved forward and allowed his head to brush Kristoff's fingers. And then it came closer and nuzzled his hand. After a few minutes the reindeer was curled against his side in the snow and Kristoff was lazily brushing his hand over his fur.
"Can I give you a name?" Kristoff asked. The reindeer let out a snort in his sleep. "Okay. I like Sven. When you wake up I'll let you know that's your name."
Eventually the reindeer did wake and Kristoff carried him through the forest to save his shaky legs. He seemed to accept the name as he curled into Kristoff's shoulder and let out a snort of content.
"You'll be my brother. I never had one before but you like you haven't either. So it's perfect," Kristoff said.
Eventually Kristoff stopped carrying Sven and Sven started carrying him. And even when Kristoff refused to give Sven a carrot the reindeer stuck around. They wer each other's pillows, meal partners, wingmen, and best friends. And the strangest pair of brothers anyone had ever seen.