It could be about giving characters in the Harry Potter universe a second chance at something. Maybe a character who made a big mistake gets a chance to redo a decision. For example, if Neville Longbottom had a second chance to stand up to Voldemort earlier in the story, it could change a lot of things.
It's hard to say for sure without reading it, but it could be Harry Potter himself. Since it's a Harry Potter fanfic, he's likely to be involved. He might be the one getting a second chance at something important, like saving Sirius Black.
Obviously, Harry Potter would still be one of the main characters. Since it's about second chances, he might be dealing with things he didn't get to do right the first time. Hermione Granger would also be a key character as she's always been resourceful and could play a big role in making the most of these second chances. Ron Weasley too, as he's Harry's best friend. And perhaps some characters who were on the fringes in the original, like Luna Lovegood, could step into more prominent roles this time around.
One interesting plotline could be a character who made a big mistake in the original series getting a second chance to rectify it. For example, a Death Eater might be given a chance to turn good and fight against Voldemort. Another could be a character like Neville having a second chance to prove his worth even more spectacularly, perhaps by being the one to finally defeat Voldemort. Or it could be about Harry having a second chance to save someone he couldn't save before, like Sirius, which would lead to a whole new set of adventures and challenges.
Some fanfictions might have a plot where characters who died in the original series are brought back and given a second chance at life. For instance, Sirius Black could return and this time, he and Harry could have a proper relationship, with Sirius being able to guide Harry more effectively. There could also be a plot where the magical world as a whole is given a second chance after the destruction caused by Voldemort. New laws and systems are created to prevent such a dark wizard from rising again.
Harry Potter himself is often a main focus. Since the title has 'Second Chances', it could be about Harry getting another opportunity to deal with his past traumas or make different choices. Hermione Granger is also commonly focused on. Maybe she gets a second chance to show her intelligence in a different way or to fix a relationship that didn't work out as well in the original story. Ron Weasley too, perhaps he has a chance to be more confident or to be a better friend in these fanfictions.
The main characters could also be entirely new characters introduced in the fanfic. The author might create someone who has a unique connection to the events of the original series and is given the task of changing things. However, it's also possible that classic villains like Cersei could be main characters if the fanfic is about giving her a second chance at ruling, perhaps with a different approach this time.
In the 'Second Chances' 'Game of Thrones' fanfic, it might focus on different plotlines. For instance, it could explore how a minor character who was overlooked in the original series gets a second chance to shine. It could be that this character has some hidden power or knowledge that, with this new chance, they can use to influence the power struggles in Westeros. This could lead to new alliances and rivalries that we didn't see in the official story.
Well, a Severus Snape x OC fanfic often explores a unique relationship. In 'Second Chances', it might be about the OC getting another opportunity to interact with Snape. Maybe it delves into their past misunderstandings and how they try to overcome them this time around. It could also show Snape's complex character in a new light as he deals with this unexpected second chance with the OC.
I'm not sure specifically as I haven't read this particular fanfic in detail. But generally, in RWBY fanfics, it could involve the characters dealing with themes of redemption and new beginnings which might be related to the 'second chances' in the title.