Another theme is identity. Naruto has to figure out who he is now that he is the Kyuubi incarnate. Is he still the same Naruto? Or has this new power changed him? And how do others see him? For instance, some people might be afraid of him now that he has the power of the Kyuubi, while his friends try to support him through this change.
One popular 'naruto kyuubi incarnate fanfic' is 'The Nine - Tailed Fox's New Path'. It explores Naruto's relationship with the Kyuubi in a unique way, showing how he masters the power in different scenarios.
One common theme is power. How Naruto harnesses the Kyuubi's power and grows stronger. Another theme is friendship, as the relationship between Naruto and the Kyuubi can be seen as an unusual form of friendship. And there's also the theme of redemption, like when the Kyuubi tries to make up for its past misdeeds.
One main theme is friendship. Naruto forms a bond with the Kyuubi and the Nibi, which is not common in the original series. This bond is based on mutual understanding and trust.
Power is a major theme. The Kyuubi gives Naruto immense power, and in the DxD world which is also full of powerful beings, the exploration of how this power is used and controlled is often central.
Another theme is friendship. Even though the Kyuubi starts as a somewhat hostile force, over time in fanfiction, a friendship or at least a mutual understanding can develop between Naruto and the Kyuubi. This is seen in stories where they work together to overcome challenges.
One common theme is power. Since Kyuubi is a source of great power, many fanfics explore how Naruto uses or struggles with this power. Another theme is friendship. Despite their initial enmity, they can become friends in the fanfics.
Isolation is also a theme. Because of the Kyuubi, Naruto is often ostracized by the villagers when he's young. Fanfics might focus on how he copes with this isolation, whether it's by finding solace in his own training or by forging unlikely friendships despite the villagers' attitudes. This theme adds depth to the character of Naruto in the context of the young kyuubi situation.
Power and control. Since it involves the Kyuubi's power and a zanpakuto, a major theme is how the character controls these powerful forces. For example, Naruto has to constantly struggle with the power of the Kyuubi in the original series, and adding a zanpakuto to the mix makes it even more complex.
One main theme is the relationship between the innocent and vulnerable baby Naruto and the powerful, yet somewhat trapped Kyuubi. It shows how two very different entities co - exist.
One common theme is identity. When Naruto and Kyuubi swap bodies, they both have to re - evaluate who they are. Naruto has to understand what it means to be a powerful being like the Kyuubi, and the Kyuubi has to come to terms with being in a human form.