One consequence could be that it messes with the natural balance of the ninja world. Maybe the cycle of life and death is disrupted, and this causes some strange phenomena to occur, like abnormal weather or chakra imbalances.
In certain fanfic ideas, Naruto could have made a deal with some sort of otherworldly being. He might have sacrificed something of great value, like a part of his own chakra or a future ability, in exchange for Kushina's life. Another possibility is that he finds a way to reverse the very nature of death by using some unique properties of the tailed beasts' chakra that he has access to.
It's not really possible within the normal Naruto lore. But fanfiction is all about exploring 'what ifs'. In a yaoi fanfiction where Naruto brings Itachi back to life, it could be based on some extreme emotional bond. Maybe Naruto discovers a hidden power within himself that he can use to reverse death. But this goes against the established rules of the Naruto world where death is usually final. So, it's really a matter of the author's creativity and how they can justify such a huge event within the framework of the Naruto world, even if it's a yaoi - inspired take on it.
One possible plot could be that Naruto discovers some ancient and forbidden jutsu. He decides to use it to bring Mito back to life in order to gain more knowledge about the Uzumaki clan. Mito then helps Naruto understand some hidden powers within the clan and they together face a new threat to the village.
One possible plot could be that Naruto discovers a powerful and long - forgotten jutsu that has the ability to revive the dead. He decides to use it on Itachi. Once Itachi is back, they join forces to stop a new, powerful enemy that is threatening the ninja world. Itachi's skills and knowledge, combined with Naruto's power, make them an unbeatable team.
Some of the shinobi who are more traditional in their beliefs may oppose Naruto. They think that death is final and interfering with it could anger the gods or spirits. They may also fear that Mito, being from a different era, could bring with her old - fashioned or dangerous ideas that could divide the village.
One possible plot could be that Naruto, consumed by his love for Itachi (in a yaoi sense), embarks on a journey to find a way to bring him back. He might encounter some ancient and forbidden jutsu that has the power to resurrect. Along the way, he has to face many challenges and enemies who oppose his plan. Once he brings Itachi back, they then have to deal with the consequences of defying the natural order of life and death in the Naruto world, and also explore their new relationship.
She might start by using her knowledge of Naruto's past. Since she is his mother, she knows things about his early life that no one else does. She could use these memories to create an emotional connection with him. Maybe she'll show up in his dreams first, like a hazy memory, and then gradually reveal herself in the real world.
Kushina could also seek the help of other powerful shinobi. For instance, she might ask Minato for assistance. Since Minato was Naruto's father and also a very skilled ninja, together they could come up with a plan to reunite with Naruto. Maybe they would use some sort of space - time ninjutsu to get closer to him.
Yes, there are likely such fanfictions. Many fanfiction writers like to explore the idea of Itachi coming back to life with his memories intact. This allows for interesting character interactions, especially with Naruto. Itachi could use his wisdom and skills once again, and his relationship with Naruto could further develop in new and unexpected ways.