Since I don't know the exact 'locke and key sea monster story', but if it's related to the Locke and Key series, the main characters would probably be members of the Locke family. They are often the central figures in stories related to the keys.
The 'locke and key sea monster story' might be a story where the keys in the Locke and Key world are somehow connected to a sea monster. Maybe the keys are used to unlock a secret about the sea monster, like its origin or a way to defeat it. It could also be that the sea monster is guarding something that the Locke family needs to access, and they have to use their wits and the power of the keys to get past it.
The Locke family members are the main characters. They are the ones who have to deal with the horrors associated with the keys and the house.
The main characters are the Locke kids. Tyler is often the more responsible one, trying to keep his siblings safe. Kinsey is more adventurous and eager to explore the powers of the keys. Bode, being the youngest, is a bit naive but also has a special connection to some of the keys. And of course, there are also the antagonists like Dodge, who is constantly trying to get the keys for their own evil purposes.
The main characters include the Locke family members. There's Tyler Locke, Kinsey Locke, and Bode Locke. Each of them plays an important role in the story related to the keys.
There could be a fearless captain as one of the main characters. He is the one who makes the decision to chase the sea monster and leads the crew.
In the 'sea monster tf story', the main characters could be diverse. It might be a group of fishermen who witness a strange phenomenon that leads to the sea monster transformation. Or it could be a young wizard who accidentally causes the transformation while trying to perform some other magic near the sea. There could also be a sea witch as one of the main characters, either causing or trying to prevent the transformation.
The main characters are Andromeda, who was the victim to be sacrificed to the sea monster, and Perseus, the hero who saved her.
Well, the Locke family forms the core of the main characters. Tyler, being the eldest, has to take on a lot of responsibilities. Kinsey is trying to find her place and has her own growth throughout the story. Bode is the cute yet mischievous youngest. And then there's Rendell Locke, their father, whose past actions and knowledge of the keys also have an impact on the story. Dodge, as the villain, adds the conflict as he constantly tries to outwit the Locke family to get his hands on the keys.
There is also the Gentleman Bastards, the group that Locke and Jean are part of. Each member has their own skills and personalities that contribute to the overall story and their adventures.
The two key characters are Victor Frankenstein and the monster he creates. Victor is a scientist who, out of his thirst for knowledge and a bit of hubris, creates the monster. The monster, on the other hand, is a being with emotions and intelligence, but his appearance makes him an outcast in society.