One possible storyline could be Naruto exploring his new abilities. He might have to train hard to control the powers from both bloodlines. Another could be that other clans become either jealous or fearful of him. There could also be a storyline where Naruto uses his combined DNA to bridge the gap between the Senju and Uchiha, who have a long - standing rivalry.
Well, having Senju and Uchiha DNA could potentially give Naruto some amazing new powers. The Senju are known for their strong life force and chakra control, so Naruto might have even greater reserves of chakra and better control over it. As for the Uchiha DNA, it could give him access to the Sharingan or some of its related abilities like enhanced perception. This could make him an even more formidable opponent in battles.
Another aspect to explore in the fanfic is Naruto Senju's relationship with the other villages. Given his Senju heritage, there might be different expectations and tensions. He could work towards a more equal - footed relationship with other villages, instead of the traditional power dynamics. This would involve a lot of diplomatic meetings and negotiations, which could be full of drama and intrigue.
One possible plot could be that Naruto discovers he has Senju blood through some hidden family secret. He then has to deal with the implications of this new identity while still trying to achieve his goal of becoming Hokage.
I'm not sure it's a widely popular fanfic type. There are so many different directions fanfictions in the Naruto universe can take. Some are centered around the Akatsuki, others on the Uchiha clan, and so on. The idea of Naruto being a Senju fanfic might not be as mainstream as those. But it could have a dedicated following among those who like to explore unique takes on the Naruto story.
Love and relationships are common themes. Since it's a harem concept, the development of Naruto's relationships with the Senju characters is central. For instance, the growth of romantic feelings and how they deal with jealousy among the harem members.
In some 'naruto senju fanfic' stories, a Senju could be reincarnated in a different era of the Naruto world. This reincarnation would bring with it memories and skills from the past. The character then has to adapt to the new era, which may have different rules and threats. They could use their Senju knowledge to make a significant impact on the new world they find themselves in.
The uniqueness might lie in how it reimagines the Senju character as a solar prophet. In the Naruto universe, the Senju are known for their strong connection to nature and chakra. By making one a solar prophet, it may introduce new types of powers, such as the ability to harness solar energy in ways not seen before. Also, it could bring a new perspective to the Naruto world's lore and how different forces interact.
The story could focus on Naruto's character development. Under Hashirama's training, he might become more in tune with nature, similar to how Hashirama was. This could lead to Naruto having a calmer and more strategic approach in combat. Also, Hashirama could share his wisdom about leadership with Naruto, which would be beneficial as Naruto is seen as a future leader. For example, Hashirama could teach Naruto how to resolve conflicts within the village in a more diplomatic way.