Well, Harry Potter himself would most likely be one of the main characters. He's the central figure in the original series, so it's reasonable to assume he'd play a big role in the fanfic as well.
Rose Granger - Weasley is also well - liked. She inherits the intelligence of her mother Hermione and often gets into adventures with Albus and Scorpius. Her strong - willed nature and her ability to solve problems using her brains are appealing aspects in the fanfic.
It could be a long - lost relative of Harry Potter. Maybe a cousin who was hidden away for some reason and now discovers their magical heritage. They could have a different personality from Harry, like being more shy and studious but still having a great sense of justice.
Often, the children of the original characters are main characters. For example, James Potter, Albus Potter, and Lily Potter. Scorpius Malfoy is also likely to be a main character as his family has a complex history with the Potters. Then there are the new friends they make at Hogwarts, like Rose Weasley. These characters inherit the legacies of their families and face new challenges in the wizarding world.
Well, Harry Potter is surely one of the main characters, as the title implies. His development across two lifetimes would be a central focus.
In many 'In this world and the next' fanfictions, Severus Snape remains a popular character. His complex past and ambiguous loyalties in the original series make him ripe for further exploration. Fans might write about his experiences in the 'next world' or how his actions in this world are affected by the existence of the other. Another popular character could be Sirius Black. His free - spirited nature and his relationship with Harry are often explored in fan - made stories.
In the world of Harry Potter the Next Generation fanfic, James Potter II is very popular. He has that mischievous streak like his namesake. Lily Luna Potter is also well - liked. She's often depicted as having a unique magical ability or being really close to her brothers. Another popular character is Teddy Lupin. Even though he's a bit older than the main next - gen group, his connection to the original characters and his own charm make him a great addition to many fanfics.
Albus Severus Potter is quite popular. He's the son of Harry Potter and has his own set of insecurities and challenges to overcome. Scorpius Malfoy is also a favorite. His friendship with Albus is often explored in fanfics, showing a different side to the Malfoy family legacy. Then there's Rose Granger - Weasley, who is smart and strong - willed, just like her mother Hermione.
Lily Luna Potter might also be a main character. She has a strong personality and her own set of skills. Her presence in the time - travel plot could bring a different perspective, especially when it comes to interacting with the female characters from the past.
It's likely that the main characters will be the descendants of the well - known characters from the original Harry Potter series. So, in addition to the Potters, the Weasleys' next - gen kids could also play major roles. They might inherit some of the traits and skills of their parents. There could also be new characters from other wizarding families that interact with them and become central to the story as well.
I don't know for sure as I haven't read this particular fanfic. But it could have the main character be an original creation with the 'lionheart' trait, or it might center around a well - known Harry Potter character like Harry himself with some new 'lionheart' - inspired story arc.