Ron could be involved. He might be nearby when the situation occurs and try to help Harry in some way, like providing a distraction for Bellatrix. Neville could also be there. He's grown quite brave and might step in to assist Harry, perhaps by using his skills with Herbology to create some sort of plant - based defense against Bellatrix.
One possible plotline could be that Harry uses a powerful spell he's been secretly practicing to stun Bellatrix just in time as she's about to harm Hermione. For example, he might use a modified version of the Stupefy spell that's more powerful. Another could be that Harry manages to create a diversion, like summoning a horde of magical creatures, which distracts Bellatrix long enough for him to rescue Hermione.
In this fanfiction scenario, Bellatrix saving Harry from the Dursleys is quite an unexpected twist. It could be that Bellatrix has some ulterior motive. Maybe she wants to use Harry for her own dark purposes against Voldemort. She might see Harry as a valuable pawn in the power struggle within the Death Eater ranks.
In some fanfictions, Draco might save Hermione from Bellatrix out of a new - found sense of morality. Maybe he has grown tired of the Dark side's cruelty. He could see Bellatrix about to harm Hermione and use his knowledge of the Death Eaters' ways to create a distraction. For example, he might pretend that there is an intruder in another part of the manor, causing Bellatrix to leave Hermione momentarily, giving Hermione a chance to escape or for Draco to help her further.
One possible scenario could be that in this fanfiction, Harry discovers that Hermione is being bullied by some dark - minded students at Hogwarts. He steps in immediately, using his skills and the respect he has among his peers to put an end to it. Maybe he threatens the bullies with exposure to the professors if they don't stop.
In some fanfictions, Ron saves Hermione from Bellatrix in a more psychological way. He manages to get into Bellatrix's head, using a rare mind - influencing spell. He makes Bellatrix see her worst fears, which causes her to drop her wand and flee, leaving Hermione unharmed. This shows that Ron doesn't always have to rely on brute force to save Hermione. It also adds an interesting layer to his character as someone who can be clever and resourceful in different ways.
There are fanfictions where Ron teams up with other characters to save Hermione from Bellatrix. Maybe he gets help from Neville, who has also grown to be quite powerful. Together, they manage to outwit Bellatrix. Ron could use his strategic mind to create a diversion while Neville sneaks up on Bellatrix and disarms her, allowing Hermione to be freed from whatever spell or trap Bellatrix had her in.
One possible scenario is that Snape steps in during a confrontation. Bellatrix is about to harm Hermione, and Snape, using his quick reflexes and advanced magic, stops her. He could be acting out of his own sense of right and wrong, or perhaps because he has a hidden agenda that involves keeping Hermione safe.
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 thing that could happen is that the wizarding world would be in chaos. The Death Eaters would be confused by Bellatrix's actions, and the Order of the Phoenix would be very suspicious. Harry would be in a difficult position, not knowing whether to trust Bellatrix or not.