In certain fanfic concepts, Naruto could have found a special relic or artifact. This relic might have the power to reverse death. Since Naruto is always on adventures and exploring different places, he might stumble upon such an item and use it to revive Kushina. It could also be related to the Uzumaki clan's secrets that he uncovers which enables him to bring his mother back.
Perhaps Naruto finds a way to travel back in time and prevent Kushina's death in the first place. He could use his Sage Mode or some other special ability to manipulate time. And then, by changing the past, he effectively'revives' her in the present. In the Naruto universe, there are all kinds of crazy powers, so time - travel isn't completely out of the question.
One big impact would be on Naruto himself. Having his mother back would give him the family love he always longed for. He would have someone to share his problems and joys with on a more personal level.
It could change the power balance in the ninja world. Other villages might see Konoha as a much greater threat with Minato and Kushina back. On the other hand, it could also lead to more cooperation as they might be seen as a symbol of hope. Emotionally, for Naruto, he would be able to learn more about his family, his heritage, and maybe even get some long - awaited parental guidance which would further develop his character.
It could happen due to Naruto's strong bond with Kushina. His willpower and love for his mother are so great that they somehow manifest into a special ability. In some fanfic concepts, Naruto's unique chakra, which is a combination of his Uzumaki and Namikaze heritage, could have some latent power that he unlocks when he is at his most desperate moment to see his mother again. This power then allows him to revive Kushina.
Jiraiya could also be involved. Maybe before he died, he left some sort of prophecy or clue about reviving the dead. Naruto could remember something Jiraiya said or find a hidden scroll that Jiraiya left specifically for this purpose. And Jiraiya's connection to the toads might also provide some sort of magical or spiritual assistance in the revival process.
In certain fanfiction concepts, Naruto might make a deal with some sort of spiritual entity. He sacrifices something of his own, like a part of his power or his future, in order to bring Kushina and Minato back. Or he could have harnessed the power of the tailed beasts in a new and unique way. The tailed beasts are extremely powerful, and if he could combine their power with his own in a specific way, it might be enough to revive his parents.
One consequence could be that Naruto is seen as a hero by some, but also as a rule - breaker by others. The ninja world has rules about bringing back the dead, and Naruto's actions might stir up controversy. Some might fear that this new ability of his could be misused. Haku, on the other hand, would have to adjust to a world that has changed since his death. He might face challenges in reconnecting with his old friends or finding his place in the new ninja world.
Another aspect could be that the fanfiction delves into how Kushina's presence affects Naruto's relationships with others. For instance, his relationship with Sasuke could be different. With a strong maternal figure in his life, Naruto might be more stable emotionally and be able to approach Sasuke in a more understanding way, which could potentially change the whole dynamic of their rivalry and friendship.
In the Naruto universe, bringing someone back from the dead is extremely difficult. While there are some jutsu like the Edo Tensei that can reanimate the dead, it has its limitations and is often considered dark magic. For Naruto to revive Jiraiya, he would need to find a way around the natural laws of life and death. However, in fanfiction, anything is possible as it allows for creative interpretations and bending of the established rules.