Obviously, Bruuce and Wanda are the main characters. Bruuce is presented as someone who is in an angry or confrontational mood as indicated by the 'go ahead and piss me off' part. Wanda, on the other hand, might be a character who is either going to react defensively or try to defuse the situation depending on her character traits, which we can assume will be explored in the fanfic.
The main characters are clearly Bruuce and Wanda. Bruuce seems to be the one taking the more aggressive action by grabbing Wanda, and Wanda is the one on the receiving end of this action.
The 'bruuce grabs wanda go ahead and piss me off' part of the fanfic title might suggest that Bruuce is in a very volatile state of mind. He grabs Wanda, which is a very aggressive action. This could be the start of a story where Wanda tries to figure out why Bruuce is so angry with her. Is it related to a past event? Or is it a misunderstanding? The fanfic could explore their relationship dynamics, how they communicate or rather fail to communicate in this tense situation, and how they might resolve the conflict or make it worse.
Filch could be a key character too. Harry going back in time might mean more opportunities to outwit Filch and his attempts to catch students misbehaving. This would add a lot of comical moments as Filch is always so serious about his job and Harry could use his time - traveling knowledge to drive Filch crazy with his pranks.
Vision would be an obvious choice as they have a deep connection. Another could be Doctor Strange. Their different magic - based powers could create an interesting dynamic. And then there's Pietro, her brother. A story about their reunion in a different context could be really engaging.
It could be Orochimaru. He's always been interested in powerful bloodlines, and the Uzumaki's power would be no exception. He might try to do something to Naruto that would piss off an Uzumaki, like trying to steal his chakra or use him for some evil experiment.
Obviously, Madara (or his Limbo clones) and Sakura are the main characters based on the title.
Obviously Naruto would be one of the main characters since it's a Naruto - centered fanfic. Sakura might also be a key character, perhaps she helps Naruto in his journey of letting go. And Sasuke could be involved too, as his relationship with Naruto is so central to the Naruto series.
You could have Zuko be constantly outsmarted by his enemies in really dumb ways. Also, you could make his backstory completely different in a bad way, like making his mother leave him because she didn't love him. And then, you could make him lose his temper at every little thing, which is not in line with his growth as a character in the original story. This would really get on the nerves of Zuko fans who love his character development.
One way could be to make Zuko constantly lose his battles in a really uncharacteristic and stupid way. Another way might be to give him a really cheesy and out - of - character love interest. And a third way could be to have his father be nice to him all of a sudden for no good reason.
The main characters are obviously Vision and Wanda. Vision is an android with a unique personality and abilities. Wanda, also known as Scarlet Witch, has powerful magic. In the context of this fanfiction, they are in a relationship and expecting a baby.
One possible fanfic could be where Wanda is on the bridge during a chaotic battle in 'Age of Ultron'. As she stands there, she realizes the danger she's in and decides to get off. She uses her powers to create a distraction among the enemy forces and then quickly makes her escape. Maybe she levitates herself down to safety, all while the battle rages on above her.