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.
One popular 'naruto senju harem fanfic' could be 'Naruto: Senju's Legacy'. It has an interesting plot where Naruto is involved with the Senju clan in unique ways within the harem concept.
One major ethical concern is the idea of slavery. Slavery is an immoral and unjust institution in real life, and depicting it in fanfiction, even in a fictional Naruto - based context, can be disturbing. It normalizes a relationship based on coercion and lack of freedom. Also, the harem aspect might objectify characters, reducing them to simply being part of a collection for the pleasure of one character, which goes against the principles of respect and equality for all characters.
I'm not entirely sure if it's a highly popular genre. While the Naruto fanfiction world is vast and diverse, the idea of a'slave harem' concept might not be as mainstream as other themes like adventure or character development. It could appeal to a niche group who are interested in exploring such unique and often controversial relationship dynamics within the Naruto universe.
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.
Tsunade could be part of it. Since she is a Senju, she could be a powerful ally and also someone who helps Naruto and Hinata navigate the complex relationships in the harem. Also, Nawaki Senju could be brought back in some way, maybe as a spirit or through some time - travel plot device. He could befriend Naruto and be involved in the growth of the relationships within the harem.
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.
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.
One idea could be Naruto, who has a connection to the Senju clan, finds himself in a harem situation with Hinata. Maybe they all have to go on a quest to protect the village, and during this journey, their relationships develop. For example, Hinata could use her Byakugan to help them avoid traps while Naruto uses his Senju - related powers to fight off enemies.