Nothing was the same after his parents' deaths. Kristoff's uncle stayed with him for a while until he had to be sent to an orphanage when he turned five years old. But he was an adventurous kid and he explored the woods a lot. He did run away from the orphanage and met Sven, who was an orphaned baby reindeer. They stuck together for years and became best friends.
Every time there was a rainstorm, Kristoff would hide his face in Sven's fur and whimper from the nightmares he kept on getting. Sven noticed one night and comforted his owner. Kristoff smiled a bit and he had gone to sleep peacefully without any nightmares that night. As he grew up, he wrote a lullaby for him and Sven, but he had learned how to sleep in different kinds of weather, so the lullaby was just for Sven.
That is, until he met Anna and Elsa.
It had been a long time since he could call many people his "friends" and the trolls didn't really count. He was somewhat a loner after he was adopted by the trolls when he was eight years old. He didn't really care about what people thought about him and he didn't really have good times with other people. He was perfectly fine with being alone until he fell in love with Anna. He finally knew someone who cared about him and that made him happy. When the storms had appeared, his nightmares had come back, but they were worse than the ones he had when he was little.
What was different about the nightmares? What if he was on the ship with his parents? He wouldn't have survived that storm either. Was he alone again? Kristoff spent the night, trying to calm himself down, but he couldn't calm down. He left his room and walked into the gallery. He looked at the picture that Elsa had given Anna for her 19th birthday.
"Hey, Kristoff," the Princess said, standing next to him. He looked at her and gave her a weak smile. "Are you okay?"
"I'm fine," he replied harshly.
"No, you're not," replied Anna, stubborn as ever.
"Yes, I am," he said, walking away.
"What's wrong with you?" Anna snapped at him.