Temari, Gaara's sister, is also very likely to rush to his side. She is protective of her younger brother and has great combat skills. She would be there to both defend him from further harm and to help him heal, using her knowledge of medical ninjutsu if she has any.
The entire Sand Village would probably come to Gaara's aid. As their leader, he is highly respected. The ninja of the Sand Village would see it as their duty to protect him. They would form a perimeter around him, fend off attackers, and do whatever it takes to ensure his safety and recovery.
Liz and Patty would be the most obvious ones. They are his weapons and also his friends. They are always by his side and would do anything to protect him. So when he gets hurt, they would be right there to try and help him, whether it's by fighting off any remaining threats or trying to find medical help.
Jiraiya, if he were still alive in the fanfiction, would be a crucial character to help Naruto. He was Naruto's mentor and had a vast amount of knowledge. He could use his sage techniques to both protect Naruto and find a way to heal his wounds. Tsunade, as the Hokage, would also mobilize all available resources in the village to ensure Naruto's safety and recovery. Shikamaru, being one of the more intelligent characters, would come up with plans to deal with the situation while Naruto is wounded.
Gajeel is very likely to come to her aid. He has a special bond with Levy, so when she gets hurt, he would be one of the first to rush to her side. He might use his iron dragon slayer magic to protect her from further harm or carry her to safety.
Beast Boy would definitely be one of the first to react. He and Raven have a special bond in the Teen Titans, so if Raven gets hurt, he would be extremely worried. He might use his shape - shifting abilities to quickly get to her side or try to find help.
Even some of the enemies of the Kanes could be involved in a different way. For instance, if Carter was hurt by a particular enemy, that enemy would be a central figure in the fanfiction. But there could also be unexpected allies among the enemies. Maybe a lower - ranked enemy realizes that Carter's death or continued injury could lead to a worse situation for them all, and they end up helping in some way, either by providing information about the cause of the injury or by secretly protecting Carter from their more evil comrades.
Erak might be an unexpected character to help. Despite his rough exterior, he has a sense of honor. If he happened to be in the area when Will gets hurt, he could offer his ship as a means of quick transport to a place where Will can be treated. Also, the apprentices that Will has trained. They would look up to him and would be eager to repay his kindness. They could run errands, gather herbs for medicine, or keep watch while Will recovers.
Alex is very likely to be one of the first to help Kara. As her sister, she has a deep bond with Kara and would do anything to protect her. Alex has medical training and combat skills, so she can both treat Kara's injuries and defend her if needed. Another character would be Winn. He is a tech - genius and could use his knowledge to create something to help Kara heal faster or to find a way to counter whatever caused her injury. Also, J'onn J'onzz, with his shape - shifting and telepathic abilities, could be a great asset in protecting Kara while she's injured and in helping her recover mentally as well as physically.
Hermione would definitely be one of the first to help. She's extremely intelligent and well - read in magic, so she'd quickly start looking for spells or potions to heal Harry. She'd also stay by his side to comfort him and keep his spirits up.
Katara would be a likely character to help Toph recover. Katara is a waterbender and has healing abilities. She would use her skills to tend to Toph's injuries, whether they are physical wounds or internal damage from overusing her earthbending. Another one could be Aang. He's the Avatar and has a deep connection with all the elements. He might use his spiritual knowledge to help Toph heal faster, maybe by finding a special place for her to rest and regain her strength.
In some fanfictions, Jane Foster could play a role. If she's around Asgard at the time, being a scientist, she might have some knowledge or technology that could be used to treat Loki's wounds. Also, Valkyrie could be a helper. She's a fierce warrior and has a sense of honor. She might see Loki's injury as a chance to prove her worth or as a debt she needs to repay if Loki had previously helped her in some way. And of course, Frigga, if she were still alive in the fanfiction, would be a great source of comfort and healing magic for Loki.