A very popular plot is that Naruto has already mastered the Nine - Tails' chakra to an extent that he can manipulate it in ways others can't. He uses this mastery to enter the Kyuubi's lair within himself and finds Kushina there. He then battles the Kyuubi's inner darkness and overcomes it to save Kushina. There are also fanfictions where Naruto has some sort of prophetic dream about Kushina's situation and he uses this knowledge along with his skills and powers to save her from the Kyuubi.
Often, in these fanfictions, Naruto has a hidden power that is related to his Uzumaki heritage. This power awakens when he realizes Kushina is in danger from the Kyuubi. He then uses this power to not only save Kushina but also to tame the Kyuubi in a way that no one has ever done before. It could also be that Naruto has made a deal with some other powerful entity that gives him the means to save Kushina from the Kyuubi.
One common theme is family. Since Kushina is Naruto's mother, fanfictions often explore the family bonds. They might show how Naruto's connection to Kushina affects his relationship with the Kyuubi. Another theme is power. The Kyuubi's power within Naruto is a huge aspect. Fanfictions may deal with how Naruto learns to control it, and how Kushina's own experiences with the Kyuubi's power can help or hinder Naruto. Redemption can also be a theme. The Kyuubi, which was once seen as a monster, could be redeemed through its relationship with Naruto and the influence of Kushina's memory.
One common plot is that Hinata arrives at the crucial moment when Naruto is about to be defeated by Pain. She uses her Byakugan in a new and unexpected way to counter Pain's attacks. For example, she might be able to see a weakness in Pain's jutsu that no one else could.
Well, Naruto could save Kushina from the Kyuubi in fanfiction through his strong willpower. We know Naruto has an unbreakable spirit. He might be able to communicate with the Kyuubi in a different way, like showing the Kyuubi a future where it doesn't have to be so violent. And by doing this, he could convince the Kyuubi to release Kushina. Also, Naruto might have received some special power or training that enables him to counter the Kyuubi's attack and save Kushina.
Another plot is where the girl is in some sort of self - imposed danger, like she's lost in a dangerous area or has made a deal with a bad guy. Naruto then has to use his wits and strength to not only save her physically but also get her out of the bad situation she got herself into. In some fanfictions, this also leads to the girl having a change of heart and becoming a better person thanks to Naruto's influence. This plot is interesting as it shows Naruto as a positive influence on others.
A 'Kushina Saves Naruto' fanfiction could also feature Kushina being in Naruto's mindscape. She could guide him through some difficult mental challenges, like when he was struggling with the Nine - Tails' power. By using her maternal love and knowledge, she helps Naruto gain better control over his power, saving him from being consumed by the Nine - Tails' negative influence.
One common plot could be Naruto having a difficult past because of Kushina's actions in the fanfic world, which leads to his hatred. And for the 'love' part, it might be Naruto finding love with a new character who helps him heal from the pain caused by his relationship with Kushina. For example, a kind-hearted shinobi who shows Naruto what true family or friendship is like.
One common theme is power. Since both Kushina and the Kyuubi have significant power, fanfictions often explore how they control and use it. For example, they might team up to fight a greater evil that threatens the village.
These fanfictions can have a big impact. They give fans a chance to explore 'what - if' scenarios. For example, seeing Kushina save Naruto allows fans to imagine a different kind of family dynamic in the Naruto world. It can also add more emotional depth to Naruto's character as he gets to interact with his mother in ways that the original series didn't show.
Well, a frequent theme in these fanfictions is self - discovery. As Naruto tries to save the fem Kyuubi, he often discovers new things about himself and his abilities. Also, the theme of redemption can be present. Maybe the fem Kyuubi has a past she wants to atone for, and Naruto's actions help in that process. It's all about how their relationship evolves during the saving process.
Maybe it's because Naruto has some sort of special connection or resemblance to the Kyuubi that Kushina notices. For example, Naruto might display some of the Kyuubi's power characteristics in an obvious way that makes Kushina jump to that conclusion.