There's a chance that the fanfiction might introduce an original character who becomes an important part of the Glee club. This new character could interact with the existing ones and change the dynamics, which would be in line with the 'glad you came' theme as they bring something new to the group.
Perhaps it involves a love triangle within the Glee club members. One character is torn between two others, and their feelings develop in unexpected ways, which can be related to the idea of unexpected arrivals or changes as hinted by 'glad you came'.
The main characters would include Kurt Hummel. He would probably be in charge of the decorations, making the dinner area look fabulous. Mercedes Jones would be there, bringing her amazing voice and her big heart. Puck would also be involved, maybe causing a little bit of chaos at the dinner table but in a fun way. And Quinn Fabray, who might be reflecting on how much her life has changed since last Christmas.
I think Santana and Brittany would also be important characters. They are very influential within the group. Santana's sassy attitude and strong vocals would make her a force to be reckoned with when the kids take charge. Brittany, with her unique dancing skills and her own brand of charm, could contribute in her own special way. Maybe they take charge of creating a really cool dance routine for the glee club's next big show.
In 'glee', characters like Rachel Berry would likely be a main character. She's very outspoken and talented, so she could have some great interactions with the Irwins. And from the Irwin side, Bindi or Terri Irwin could be main characters as they are well - known in the Irwin family.
Jacob Black could also be a main character. His relationship with Bella and the werewolf pack's connection to the Cullens might be explored in a new light in this fanfiction. Maybe his transformation or his knowledge of the supernatural world comes into play earlier than in the original story.
I think Santana would be a key character. She has such a strong personality and her development from a bully to a more empathetic person could continue in the future story. Brittany might also be in the spotlight as she's always been a bit of an enigma and her relationship with Santana could be explored further. Additionally, Mr. Schuester could be important as he could be the guiding figure for the new generation of glee clubbers or dealing with his own post - glee club life.
I think Quinn and Black Widow would be an interesting pair. Quinn is used to being in a position of power and popularity in the Glee club, and Black Widow is a strong female character in the Avengers. They could have some really cool exchanges about strength and femininity.
In my opinion, it would probably be Kurt from Glee and Darren Criss (who is associated with Starkid). Kurt is very fashion - forward and has a strong passion for performing arts. Darren Criss is known for his incredible talent in Starkid productions. Their shared love for music and the stage would likely draw them together first.
Definitely Harry Potter and Finn Hudson. Harry is the hero in the wizarding world, and Finn is a key figure in the Glee club. They could bond over their leadership roles. Harry could teach Finn some magic tricks, and Finn could show Harry how to be more confident while performing in front of a large audience.
Finn is very likely to be involved. If he's the father, he would have a huge role in the story. He'd need to deal with his own feelings about becoming a father so young and how it affects his football and Glee club activities. Quinn could also be involved. She might offer Rachel advice based on her own experience with pregnancy, even though their situations were different. And of course, Mr. Schuester would be there. He'd be like a mentor to Rachel, guiding her through the tough times and making sure she still has a place in the Glee club.