Fred could have had some sort of pre - planned strategy. He might have been secretly observing Bellatrix and when he saw her about to harm Hermione, he used a powerful shielding charm around Hermione first. Then, he could have used a binding spell on Bellatrix to immobilize her temporarily and get Hermione out of there.
Perhaps Fred was working with a group of allies in the fanfiction. They all coordinated an attack on Bellatrix. While some of them engaged her in a magical duel, Fred was able to sneak up on her and rescue Hermione. He might have used a special charm or potion that nullifies Bellatrix's dark magic for a short time to ensure a safe rescue.
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.
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, in many such fanfictions, Harry might use his magic skills. He could cast a powerful stupefy spell on the troll to stop it in its tracks and then quickly lead Hermione to safety. Maybe he also uses his quick thinking and knowledge of the Hogwarts corridors to find a hiding place where the troll can't reach them.
In some versions, Hermione might use her advanced magic knowledge. She could have discovered a spell that counteracts the pull of the veil. Maybe she found a way to disrupt the dark magic associated with it and was able to pull Sirius back from the brink just in time.
Well, perhaps he uses his influence in the wizarding world. Maybe he has some connections or knowledge that allows him to intervene and get Hermione out of the abusive situation. For example, he could use his status among the pure - blood families to put pressure on the abusers.
Well, in some versions, Ron might use his quick wit and knowledge of Hogwarts' secret passages to outmaneuver Draco. He could lead Hermione to safety through a passage that Draco doesn't know about.
Hermione's character could develop in terms of her relationships. Through saving Fred, she might form a stronger bond with the Weasley family. She may also become more empathetic as she experiences the fear of losing someone dear. She realizes that there are things more important than just academic knowledge. So, she starts to balance her intellectual side with her emotional side more effectively.
In the fanfiction, it could be that Ron is consumed by jealousy or a false belief. This causes him to lash out at Hermione in a way that endangers her. Fred, having a protective streak, especially towards his friends, jumps into action. He might engage Ron in a duel of sorts, not with the intention to harm but to subdue him long enough to break whatever spell or negative emotion has a hold on Ron and thus save Hermione.
She likely becomes more confident in her abilities outside of just academic knowledge. Saving Fred would require her to take risks and trust her instincts, which could make her more self - assured. For example, if she has to perform a spell she's not entirely sure about, but does it anyway to save Fred, it shows her growth in believing in herself.
Well, perhaps Snape uses his position as a teacher to step in. He could have been observing the situation secretly and when Draco was about to do something harmful to Hermione, Snape intervened with a firm command or some magic spell to stop Draco in his tracks.
Well, it could be that Lucius uses his powerful influence in the wizarding world. Maybe he intimidates Ron with threats related to his family's status or he uses some dark magic to create a distraction and whisk Hermione away.