Since we have no information about the 'a kink in the armor fanfiction' other than its title, the main characters could be anyone. It could be a group of friends where one of them has this 'kink in the armor' and the others gradually come to realize it. Or it could be a mentor - student relationship where the student discovers a flaw in the mentor that is the 'kink in the armor'. There are so many possibilities depending on the genre and the source material of the fanfiction.
I'm not sure specifically as there could be many different interpretations of 'a kink in the armor fanfiction'. It could be about finding a flaw or unexpected element in a character's otherwise strong 'armor' (metaphorically), like a hero having a secret weakness that gets explored in the fanfiction story.
Obviously, Spider - Man himself is a main character. He's the one who wears the spider armor. There might also be his usual supporting characters like Mary Jane or Aunt May, who could have different reactions to the new armor.
Since we don't have much information about this fanfic, the main characters could be various. It might be a group of adventurers, where one of them is wearing the armor. Maybe there is a female character who is an expert in water - related magic or technology and she teams up with the armored male character. Another possibility is that the main character is a young person who discovers an ancient armor in a watery cave and then has to deal with the consequences of wearing it in the water - filled world around them.
If we assume that the 'Armor King Story' is set in a fighting - game - like universe similar to Tekken, then aside from Armor King, there could be other important characters. There might be his arch - enemy, who could be another powerful fighter with different motives. There could also be a mentor - like figure from his past who taught him the ways of combat. Additionally, there might be characters that he has to protect, such as innocent bystanders or a love interest that adds more depth to his story.
Well, apart from Ladybug and Chat Noir, other characters like Alya and Nino can also be main characters in Miraculous Ladybug Armor Fanfiction. Alya might be involved in helping Ladybug with the armor, perhaps using her skills as a journalist to uncover secrets about it. Nino could be there to support Chat Noir, and they might all work together when it comes to using or protecting the armor. Sometimes, even the villains can be main characters in a sense, as the story could revolve around their attempts to steal or destroy the armor.
Harry Potter himself is often a main character in such fanfiction. He might be the one to discover or be given the special armor. Hermione could also be involved, perhaps using her intelligence to study and improve the armor's magical properties.
It could be a young hero. In many such novels, there is a protagonist who is initially inexperienced but gradually becomes stronger with the help of the star armor. There might also be a mentor figure who guides the main character in understanding the power and significance of the star armor.
Sasuke could also be a main character in such a fanfic. Maybe he is initially jealous of Naruto getting the chakra armor and there could be a rivalry between them as they both try to master the power it offers. And Sakura might also be involved, perhaps as the one who helps heal the wearer of the armor when they get injured during battles or training.
Harry Potter himself could be one of the main characters associated with dragon armor. He's always getting into dangerous situations, and dragon armor could be something he discovers on one of his adventures. Another could be Hermione. With her love for knowledge, she might be the one to research about the armor's history and properties.
In many 'female shining armor fanfic', there could be a mentor figure for the female knight. This could be an old, retired knight who imparts wisdom and skills to her. Additionally, there might be a love interest. This character could be a noble from the court or another adventurer. Their relationship with the female knight can be a central part of the story, adding an emotional aspect to the action - filled plot.