Another possibility is Marceline. She has her own dark side, just like the Ice Prince has his cold and aloof side. They could bond over their similarities. Marceline could also introduce the Ice Prince to different music and a more carefree lifestyle. They might start out as reluctant friends but grow to really care about each other as they go through various adventures together in the Land of Ooo.
A possible plot for an Adventure Time Ice Prince fanfiction might be that the Ice Prince decides to explore the warmer parts of Ooo. He's never been there before and is curious. But once he gets there, he realizes he can't control his ice powers well in the heat. He accidentally freezes some important things and has to make amends. Finn and Jake get involved to help him learn to control his powers in this new environment. It could also be a story about him learning about different cultures in the warmer regions.
One great example could be a fanfiction where Finn and the Ice Prince have to team up to save Ooo from a new, powerful enemy. In this story, Finn's bravery and the Ice Prince's ice powers complement each other in unexpected ways. They start off as reluctant allies but gradually develop a mutual respect as they face various challenges together.
They could also be portrayed as friends from different worlds who are trying to find common ground. The Ice Prince comes from a cold, isolated place, and Finn from a more adventurous and social world. A fanfiction could explore how they bridge this gap and create a unique bond that combines their different personalities and values.
The Ice Princess stood in her glacial domain, her icy hair flowing like a frozen waterfall. She was lonely, as always. One day, Finn and Jake came by on an adventure. They were initially cautious, but Finn's kind heart reached out to her. Jake, with his goofy charm, made her laugh for the first time in ages. They decided to have a snowball fight, and the Ice Princess found herself truly enjoying the company. This simple encounter changed her view of the outside world.
The Lumpy Space Princess could also be paired with the Ice King. Her sassy attitude could contrast with the Ice King's craziness. In a fanfiction, they could end up on an adventure together where the Lumpy Space Princess tries to 'fix' the Ice King or just uses him for her own gain in a really comical way.
Well, in the Adventure Time Ice King story, Ice King is a complex figure. He lives in his ice castle. His obsession with princesses is a big part of his character arc. This is related to his past as Simon, who was in love. As Ice King, he's constantly causing chaos in the Land of Ooo. But underneath all that, there's still a bit of the old Simon left, and we can see that in some of his more tender moments, like when he takes care of his penguins.
The unique element is often the exploration of Finn's different personality in his ice form. He can be more cold - hearted in a literal sense, which creates interesting conflicts.
One common theme is redemption. Many fanfics explore the Ice King's past misdeeds and his attempts to make up for them. For example, he might try to apologize to Princess Bubblegum for all the times he kidnapped her.
One interesting 'Adventure Time Ice Queen' fanfic could be about her backstory before she became the Ice Queen. It might explore how she got her powers and what led her to be so cold - hearted.