One plot idea could be a crossover where the female Kyuubi and female Shukaku are somehow transported to the FF7 world. They could team up with the FF7 characters to fight a common enemy, perhaps a new threat created by a combination of Naruto -verse and FF7 -verse magic or technology.
Another plot could involve a love triangle between a Naruto character, a FF7 character, and the female Kyuubi or female Shukaku. For example, Cloud from FF7 might be attracted to the powerful and mysterious female Kyuubi, while Naruto has his own feelings for her, creating a complex relationship dynamic.
One common theme is the power struggle. Since Kyuubi and Shukaku are powerful entities in Naruto, when they are in female forms in fanfiction, their power and how they interact with other characters in terms of power dynamics can be a big theme. For example, they might have to fight against villains who want to use their power.
One plot idea could be that the female Kyuubi has some kind of connection to the world of FF7. Maybe she holds the key to a powerful materia that both the Naruto world and FF7 world are after. Gaara and female Shikaku could be involved in protecting her as she tries to figure out how to use or hide this power. This would bring in elements of both Naruto's ninja battles and FF7's materia - based magic system.
A possible plot is that the female Shukaku is captured by an evil organization. Naruto, being the hero he is, sets out on a rescue mission. Along the way, he discovers more about the female Shukaku's past and her connection to the history of the ninja world. This could involve ancient secrets and prophecies related to the tailed beasts.
A simple fanfiction could be that the female Kyuubi and female Shukaku start to communicate telepathically across different worlds. They realize they have more in common than they thought and decide to help each other. The female Kyuubi could offer some of her power to help the female Shukaku control her more chaotic tendencies, which in turn benefits Gaara.
One idea could be that the female Shukaku has been living in hiding among the Leaf Village. Naruto discovers her secret and they form an unlikely bond as they train together to control her Shukaku powers. This bond then turns into a deep friendship that might lead to more as they face various threats to the village.
Another option is to join Naruto or FF7 fan communities on social media platforms like Reddit or Facebook. There, you can ask other fans if they know of any good fanfictions involving these elements. They may be able to recommend some hidden gems that you wouldn't find through a simple search.
Perhaps a plot where the female Kyuubi has to take on a human form to protect Naruto from a new, powerful enemy. In the process, they develop feelings for each other while fighting side by side.
You can try fanfiction websites like FanFiction.net or Archive of Our Own. These platforms have a wide variety of fanfictions, and you can use the search function to look specifically for stories related to Naruto, FF7, female versions of Kyuubi and Shukaku. Just type in relevant keywords and browse through the results.
One idea could be exploring the relationship between the Jinchuuriki and Shukaku in more depth. Maybe the Jinchuuriki tries to communicate with Shukaku in a different way than in the original series, leading to new powers or understandings. Another plot could involve the Jinchuuriki being targeted by a new group who wants to use Shukaku's power for their own evil purposes. The Jinchuuriki then has to fight not only to protect themselves but also to keep Shukaku from being misused.
One plot idea could be that in the fanfiction, the female Kyuubi gets jealous when Naruto spends too much time with his other friends or comrades. This could lead to some tense moments where she acts out in her fox - like ways, perhaps causing a bit of chaos in the village. Another idea is that Naruto starts getting closer to a new female character, and the female Kyuubi's jealousy drives her to reveal her true feelings for Naruto in a very dramatic way.