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.
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.
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.
In fanfiction, this could be due to an alternate reality or a dark twist in the plot. Maybe Kushina was mind - controlled by some powerful enemy. It's a very strange and dark concept that goes against the normal Naruto storyline where Kushina is Naruto's mother and loves him dearly.
In some fanfictions, it might be due to an alternate timeline or reality. A change in the past could lead to Kushina having different beliefs or loyalties. It could also be related to a new power or curse that affects her judgment and causes her to see Naruto as an enemy. However, this is often a very dark and dramatic turn in fanfiction stories.
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.
Well, in a fanfiction, it might be due to a curse. There could be a curse placed on Naruto that slowly transforms him into Kushina Uzumaki. This curse could be related to some dark secret in the Uzumaki clan's past. Or perhaps a strange experiment by Orochimaru or another rogue ninja that goes wrong and causes Naruto to take on Kushina's form and some of her abilities.
One way it could happen is if Naruto somehow gains the ability to travel back in time. Maybe through a powerful jutsu or a unique kekkei genkai. He could then use his knowledge of future events and his combat skills to save his parents from their tragic fate.
Well, Naruto could be the first to notice the fire and immediately start trying to rescue any trapped people. Kushina might have some special knowledge about the cause of the fire due to her connection with the Uzumaki clan. Tsunade would use her leadership skills to organize the rescue efforts.
A great scenario in this fanfic could be that Kushina helps Naruto unlock some new hidden power. Since she was also a jinchuriki, she has unique knowledge. They could bond over their shared experiences with the Nine - Tails. Also, Kushina could play a role in mending any remaining family - related issues Naruto has, like making him feel more connected to his Uzumaki heritage.
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.