It's hard to say for sure, but perhaps the main characters are a couple of siblings. The older sibling might be protective of the younger one when it comes to the idea of sharks. And there could be a new kid in town who joins them in their exploration of the shark world. They all together form the main characters who drive the plot of the 'Shark Kids Story'.
In the 'Shark in the Dark Story', the most obvious main character would be the shark. But depending on the nature of the story, there could be other important characters too. If it's a story about the shark's journey, perhaps there could be a seagull that the shark sees flying above the water's surface during the day before it goes into the dark depths at night. Or there could be an old, wise octopus that the shark encounters in a dark cave, and they have some sort of interaction. Maybe there are also other sharks that the main shark has a relationship with, like a rival or a mate.
Since we don't know the exact story, it could be the friendly shark itself as the main character. There might also be other sea animals like fish, dolphins, or turtles that interact with the shark and are important characters in the story.
Since I don't know the story well, I can't say for sure. But the shark must be one of the main characters.
Perhaps the kids shark story's main plot is about a shark that washes up on the beach. The kids are the first to find it. They try to keep it alive until the adults can come and help. While waiting, they start to tell the shark stories as if it can understand them. And in a strange way, the shark seems to respond, and this interaction becomes the heart of the story.
Since I don't have access to the story, the main characters could be a fisherman who gets into trouble and becomes shark bait. Or it could be a group of surfers where one of them is in a situation that makes them seem like shark bait. There could also be a marine biologist in the story who is studying sharks and somehow gets too close to the sharks and becomes the so - called 'shark bait'.
Given the title 'shark girl tf story', the obvious main character is the shark girl. But there could be other supporting characters. For example, if the story is set in a coastal town, there might be fishermen who have seen strange things related to the girl. Or if it's a story about her fitting into a new world, there could be other 'creatures' or people in that world who interact with her. There could also be a mentor - like figure who helps her understand and control her new form or abilities if it involves a transformation.
I'm not sure as I haven't read this novel. So I can't tell you who the main characters are.
I think the shark must be a main character. And perhaps there could be some people in the park as well. They would be important as they might be the ones who interact with the shark, either by trying to avoid it or being curious about it.
Perhaps the main characters are siblings. A brother and a sister who have to face some challenges together. The brother could be the more adventurous one, always getting into little troubles, while the sister is the smart one who figures out solutions. There might also be their pet dog that tags along in their adventures and plays an important role in the story.
The kids shark story could be about a group of kids who encounter a friendly shark while on a beach adventure. Maybe they first see its fin in the water and are scared, but then they realize the shark just wants to play and it leads them to a hidden cove full of beautiful shells.