Since I haven't read it, I can't say for sure. But it could be a young adventurer, a powerful wizard, or even the dragon itself.
There might be a hero who is on a quest to deal with the dragon's heart. There could also be an antagonist, perhaps a dark sorcerer who wants the power of the dragon's heart for evil deeds. And of course, if the dragon is still alive in the story, it could be one of the main characters too, with its own motives and personality, like protecting its heart from being misused or having a special connection with the protagonist.
It's possible that there is a group of characters. For instance, a band of thieves who accidentally stumble upon the dragon's heart in an icy cave. Among them, there could be a leader who has a change of heart about stealing the heart and decides to protect it instead. There might also be a character who has some sort of special ability related to ice or understanding of dragons, and they play a crucial role in the story regarding the dragon's heart.
It might be a fanfic related to a particular fantasy series or universe. The 'ice' could be part of the setting, like an ice - bound land or a frozen castle. The dragon's heart could be the key to unlocking some great mystery or power. It could also involve relationships between characters, such as a bond between a human and a dragon because of the heart. Maybe there are battles against other creatures or villains who also want the dragon's heart for their own malicious purposes.
Well, there could be the dragon lords. One might be a powerful fire dragon lord who is fierce and protective of his kind. And on the ice side, a wise ice dragon lord who is known for her strategic thinking.
One of the most memorable characters could be the young dragon trainer. He has a special bond with his dragon and is constantly defying the odds. His courage in the face of danger makes him stand out.
Since I haven't read it, I can't say for sure. But it could be a story about a lonely barista who encounters a customer with a heart of ice.
Naruto himself could be a main character. He has a natural inclination towards befriending powerful beings, and his determination would make him a great fit to interact with the fire and ice dragons. Sasuke could also be a main character, with his Sharingan potentially having some unique interactions with the dragons' powers.
I'm not sure specifically as it depends on the fanfic. But it could have a brave knight who is not afraid of the ice dragon at first sight. He might be on a quest related to the dragon.
Typically, there's the protagonist who often has a special connection to the dragon blood. This character might be on a journey to discover the true meaning and power of their dragon blood heritage. There could also be a mentor - like figure, someone who has more knowledge about the dragon blood and its implications. And of course, there are usually antagonists who either want to control the power of the dragon blood for their own evil purposes or are afraid of those with the dragon blood and try to eliminate them.
It could be a dragon rider as one of the main characters. This person might have a special bond with their dragon and be deeply affected by the fall. Another main character could be an ancient dragon sage, who has knowledge about the impending fall but is powerless to stop it.
There might be a dragon named Blaze. He could be a strong and brave character, always leading the way in battles and adventures.
There could also be a group of adventurers as the main characters. When the dragons return, they might be hired or compelled to go on a quest to find out more about the dragons. This group could consist of different races and classes, like a human warrior, an elven archer, and a dwarven miner. Their different skills and perspectives would make for an interesting dynamic as they face the challenges brought about by the dragons' return.