Another possibility could be Neville. Neville is often around Harry, and he has his own insecurities and growth arc. If he were to become Harry's hand, it could be a great way to explore Neville's character further. He could gain confidence in this strange new role, and Harry could learn to rely on Neville in a whole new way.
Hermione could also be a likely character. Given how much time she spends with Harry, there are plenty of opportunities for a magical experiment or accident to occur. And with her vast knowledge, having her as a hand could be both a curse and a blessing for Harry. He would have all that knowledge at his fingertips, literally, but also have to deal with Hermione's bossy nature even in hand form.
Perhaps Harry makes Draco his hand. This could lead to a very different dynamic. Draco, now in this odd form, would be forced to rely on Harry. They might start to understand each other better. Harry could use this situation to try and reform Draco, showing him the good in the wizarding world that he has been blind to due to his family's influence. They could work together to solve a mystery in Hogwarts that they couldn't have solved alone.
It's possible that designating his hand is related to his connection with other characters. He could use his designated hand to make a pact or connection with a new ally or even an enemy. For instance, by placing his hand on a magical stone, he could create a bond of trust or enmity depending on the situation in the fanfiction.
Nymphadora Tonks is also a great candidate. She's a Metamorphmagus, which means she can change her physical form. In hand - to - hand combat in fanfiction, she can use this ability to surprise her opponents. For example, she could suddenly make her limbs longer to reach further or make her body more flexible to dodge attacks more easily.
Jaime is the main character without a doubt. But other important characters could include the maesters. They might be the ones attempting to use their medical knowledge or ancient lore to figure out how to restore his hand. And Cersei is likely to be in it too. Her reaction to Jaime getting his hand back, whether it's relief, jealousy or something else, will add to the story. And don't forget about Bronn. He might be involved in some of the more dangerous or practical aspects of Jaime's quest to get his hand, like providing protection or finding necessary items.
Neville Longbottom could be a likely candidate. He has shown great courage and has been through a lot. If the situation was dire enough, Harry might train him to be a more effective fighter, bordering on a killer, to protect Hogwarts and the wizarding world.
Well, it could lead to him seeking help from a magical healer or professor. Maybe it triggers some hidden power within him.
Maybe it was given to him by a mysterious stranger. This stranger could be someone who has been observing Harry from afar and believes that he is the only one who can handle the power of the hand cannon. The stranger appears out of nowhere, hands it to Harry, and then disappears again without a trace.
His relationships could be affected. For example, if his designated hand is seen as a sign of his new power or role, some characters might be in awe of him, while others might be jealous. This could lead to new alliances and rivalries. He may also attract the attention of more powerful magical beings who are interested in his new - found ability related to his designated hand.
In some fanfictions, there could be a fight between Hermione and Bellatrix Lestrange without wands. Hermione, being the intelligent witch she is, would use her knowledge of pressure points and self - defense spells she's adapted into physical moves. Bellatrix, on the other hand, would be more wild and unpredictable in her attacks.
Sleight of hand might be a way for characters to blend in with the Muggle world. If a wizard or witch is visiting the Muggle side, they could use sleight of hand to perform what looks like normal magic tricks to Muggles, without revealing their true magical nature. This could be a great way to interact with Muggles without breaking the Statute of Secrecy. And it could also create some really interesting scenarios where the Muggle - born wizards teach their pure - blood friends how to do these 'tricks' better.