Most likely the dragon and the rose are the main characters, even though the rose is a plant, it can be personified in the fanfic.
In 'the dragon and the rose fanfic', aside from the dragon and the rose, there could be other characters too. There might be a wizard or a fairy who has some sort of relationship with either the dragon or the rose. For example, a wizard might be trying to control the dragon's actions regarding the rose, or a fairy could be the one who planted the rose in the first place and has a connection to it.
The main characters are surely the dragon and the rose. But depending on the nature of the fanfiction, there could be side characters. For instance, if it's set in a medieval - like fantasy world, there could be knights who are either trying to slay the dragon or protect the rose for some reason. Maybe there are also talking animals that serve as messengers between the dragon and the rose.
Another possible main character could be her rival. This rival could be from a different boxing school or have a completely different boxing style. Their interactions both in and out of the ring would be a major part of the story.
Typically, the main characters would still include Ruby, Weiss, Blake, and Yang from the RWBY series. However, in the Enchanted Rose fanfic, there might be new characters introduced who are somehow related to the enchanted rose, like a guardian of the rose or a character who is cursed because of the rose.
The main character, the 'rose', could be a young, idealistic person. There might be an older, more cynical character as one of the 'thorns'. There could also be a group of characters who are the 'thorns' together, like a clique that doesn't welcome the 'rose' into their midst. Without reading the actual fanfic, we can only guess based on the common interpretations of the 'rose among the thorns' concept.
Typically, Naruto is the main focus. But depending on the plot, Sasuke could also play a significant role. For example, if the rose has some connection to the Uchiha clan, Sasuke would be drawn into the story. And there could be an old sage or a fairy - like character who knows all about the rose and its powers, guiding Naruto (and sometimes Sasuke) through the events of the fanfic.
The main character is most likely the last dragon itself. But there could also be other important characters like a brave knight who tries to befriend the dragon, or a wizard who has some connection to the dragon's past.
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.
It's hard to say exactly who the main characters are without reading the fanfic. But it's likely that the hexe dragon itself is a main character. There could also be a wizard or a mage who tries to control or befriend the dragon.
Since I haven't read this particular fanfic, I can't say for sure. But it's likely that the dragon itself is one of the main characters. There could also be a dragon rider, a wizard, or other magical creatures that play important roles in the story related to the dragon's change.