There might be a love interest for Jack. In many stories, the protagonist has someone they are attracted to or in a relationship with, and this person would be an important character too. However, without reading the novel, we can't be sure of their name.
Love is likely a main theme. It often is in stories where a character has a unique heart, like a cuckoo clock heart. The story might explore how Jack, with his special heart, experiences love and relationships.
In this fanfiction, perhaps Jack Frost's heart could be frozen due to a powerful dark magic spell. This might lead to him losing his ability to spread winter cheer and instead become a cold and distant figure.
Well, the timing of the kiss can vary greatly in fanfiction. Sometimes it might happen early on to set the romantic tone, while in other stories, it could be a climactic moment later in the narrative.
A new character could be introduced as the main antagonist. For example, a powerful ice sorcerer who is jealous of Jack Frost's natural ice powers. This sorcerer might have developed a special spell to freeze Jack's heart in order to steal his powers and take over his role as the bringer of winter.
Well, it depends on the author's imagination. Sometimes, Jack's injury might lead to emotional turmoil among the characters or trigger a series of events that test their relationships.
The rated M fanfiction might contain mature themes and intense emotions. It could explore more complex and adult-oriented aspects of their relationship.