Krystal and Amber had been friends since childhood. Amber was a mischievous little kid but she always came to little Krystal's rescue. When they got into adulthood they found out that they couldn't bear the thought of losing the other and so ended up being a couple. 

 

It's been a few years since then and it's their first Christmas with just the two of them since they usually spent it with both of their families altogether.