One popular fanfiction with this plot is 'Time's Redemption'. In it, Hermione uses a powerful time - turning device to go back. She faces many challenges in the past, like avoiding detection by other characters while trying to figure out how to prevent Fred's death. It's a great read for those who love emotional and action - packed stories.
She could accidentally change other things in the past. For example, her presence might disrupt some other events that were supposed to happen. Maybe she prevents another character from getting a crucial piece of information, which then has a ripple effect on the future.
It could be a dark wizard that was previously unknown. Maybe this wizard has a grudge against Harry's family for some long - forgotten reason and is using a very subtle and complex plan to harm Harry. And Fred discovers this wizard's plot when he goes back in time.
Well, perhaps when Fred goes back, he discovers that the danger to Harry is much more complex than he initially thought. There could be a traitor among the people he thought were allies in the past. Also, Fred himself might get stuck in the past and has to find a way to get back while still ensuring Harry's safety. Maybe the time - traveling magic is being manipulated by a hidden enemy, and Fred has to figure out who and how to stop it to save Harry.
Fred could use his knowledge of the Weasley family's magic tricks and inventions. He might have some secret gadget or spell that can break through the barriers or spells that are being used to torture Hermione.
Well, it could be that Sonic goes back in time because Shadow is in a dire situation that only Sonic can prevent. This could be due to a threat from a powerful villain that managed to overpower Shadow in the past. Sonic, being the hero he is, decides to take the risk of time travel. He might have to use some sort of time - traveling device or power. Once in the past, he'll need to quickly figure out how to stop the threat before it's too late. This fanfiction idea is really cool as it combines the action - packed nature of Sonic's world with the concept of time travel.
Well, in some versions, Fred might use his quick-witted magic skills. He could cast a distraction spell to draw Bellatrix's attention away from Hermione. Maybe a spell that creates multiple illusions of himself, confusing Bellatrix long enough for him to grab Hermione and disapparate them to safety.
One great fanfiction with this plot is 'Time's Redemption'. In it, Harry uses a powerful time - turning spell he discovers in an ancient book. He has to face many challenges in the past, like avoiding detection from the Ministry's time - turner regulations. Another good one is 'Back to Save Sirius'. Here, Harry teams up with Hermione and they use a secret time - travel device left by Dumbledore.
One common pairing is with Severus Snape. In some fanfictions, when Hermione goes back in time, she may interact with a younger Snape and they could form an unexpected bond. Another is with Tom Riddle. Their interactions can be really interesting as Hermione tries to prevent him from turning into Voldemort.
Another theme is bravery. Fred and George have to be brave to face whatever is threatening Hermione. In some fanfics, they might have to go against powerful dark forces, and their courage is what enables them to succeed in the rescue.