It could be the main characters from the original story. They might be dragged into this party - filled night. Maybe the protagonist who is usually shy but has to face this wild party scenario. And of course, the antagonist could also be there, causing some trouble among the party - goers.
Perhaps there are some mysterious characters who only show up at parties like this. They could be some sort of party - loving spirits or just people with a reputation for being the life of the party. They might have their own motives for being at the party, like looking for a long - lost friend or trying to find a valuable item that is rumored to be at the party.
Well, perhaps there could be a lot of chaos and fun. People might be dancing, drinking, and having a great time in all the rooms. There could be different themes in each room, like a disco in one, a masquerade in another. And the characters from the original story could get lost in this sea of parties and have some unexpected encounters.
Fred and George Weasley would definitely be the life of the party. They are always full of pranks and jokes, and at a house party, they would be the ones to liven up the atmosphere with their humorous antics.
There could also be new characters created specifically for this fanfic. Maybe a mysterious wizard who has a connection to Hermione's family history. This new character could bring new challenges and storylines to the fanfic, while still revolving around Hermione.
Obviously, all 14 Doctors are the main characters. Each with their own distinct personalities, from the wise and somewhat eccentric First Doctor to the energetic and compassionate Thirteenth Doctor. Their companions could also play important roles. For example, Rose Tyler might accompany the Ninth or Tenth Doctor, and Clara Oswald could be with the Eleventh or Twelfth Doctor. And of course, the Doctors' archenemies like the Daleks or the Cybermen could make appearances as antagonists, which would further drive the story as the Doctors work together to defeat them.
The other dragon riders could also be in the fanfic. Fishlegs could use his knowledge of dragons and other lore to figure out if there's a dragon - related way to heal Astrid. Snotlout might initially seem more concerned with his own status but would probably end up helping in his own way, perhaps by providing some muscle when needed for tasks related to Astrid's care.
The protagonist is very likely to complain in disappointment. They usually have high hopes and big dreams in the story. So when things don't go their way, like failing to defeat the villain or losing a loved one, they would complain. For example, in a superhero fanfic, if the superhero protagonist fails to save the city from destruction, they will be disappointed and complain about their lack of power or the unfairness of the situation.
GoGo could be a main character. She's strong - willed and independent in the original Big Hero 6, and in a Yuri fanfic, she could be in a relationship or have strong emotional ties with another female character. Honey Lemon is also likely. She's kind and creative, and her personality would make her a great candidate for a Yuri - themed relationship. They could be exploring their feelings for each other in the fanfic.
Obviously, Chell is the main character. There could also be other characters from the original story that interact with Chell during her transformation into a core. Maybe some mentor - like figures who guide her through the process, or antagonists who try to stop her from achieving this new status.
Obviously, Harry Potter himself. He's the main character who is going to fight back.
It could be Hermione, if it's related to the Harry Potter universe. She is extremely brainy and would fit the description well. There might also be other new female characters who are introduced specifically in this fanfic to add more depth to the story.