Probably Finn and Jake, as they are the main characters in most Adventure Time stories.
Finn, a brave and curious human, and Jake, his magical dog buddy, are central to Adventure Time main story. Princess Bubblegum is another important character. She's intelligent and has to deal with the governance of the Candy Kingdom. The Ice King, with his ice powers and his obsession with kidnapping princesses, is also a key figure. There's also Marceline the Vampire Queen, who has her own unique personality and backstory that ties into the main story in various ways.
The main characters are Finn the human and Jake the dog. Finn is a fearless adventurer, and Jake, with his shape - shifting abilities, is always by Finn's side. Also, Princess Bubblegum, who rules the Candy Kingdom, is an important character. And the Ice King, who often causes problems for Finn and Jake.
Since it's related to Adventure Time, it's likely that Finn and Jake could be main characters. Finn, the human boy with his adventurous spirit, and Jake, the shape - shifting dog, are central to most Adventure Time stories. There might also be Princess Bubblegum, given her importance in the overall Adventure Time world, and Marceline the Vampire Queen.
The main characters are Finn and Jake. Finn is a human boy with a brave heart and a thirst for adventure. Jake is his shape - shifting dog friend, who can stretch and change his shape in all kinds of useful ways.
I'm not sure specifically about an 'Adventure Time Cup Story' as it might be a very specific or even a fan - made story within the Adventure Time universe. It could potentially involve Finn and Jake going on an adventure related to a magical cup or something similar.
Finn the human and Jake the dog are the main characters. Finn is a brave and adventurous boy, always ready for a fight or to help those in need. Jake, on the other hand, is Finn's best friend and has the ability to stretch and change his shape, which comes in handy during their adventures.
I'm not sure exactly, but probably there are characters like the tea - maker, the person who is being served the tea, and maybe some family members or friends who join in.
Since I haven't read 'the blue cup short story', I can only guess. There could be a person who owns the blue cup, perhaps an old man or a young girl. There might also be someone who is interested in the blue cup, like a collector or a thief who wants to steal it for some reason.
Since I don't know the exact 'little tea cup story', it could be the little tea cup itself as the main character. There might also be a person who owns the tea cup, like an old lady who cherishes it.
The main characters are likely Finn and Jake. They are the protagonists in the 'Adventure Time' series and would probably be the central focus in the 'Islands' novel as well.