This fanfiction might be centered around the idea of Naruto being the son of Sephiroth. It could explore how Naruto's character develops with Sephiroth's influence. For example, Sephiroth is known for his great power and his somewhat tragic and complex backstory. Naruto might inherit some of that power and have to deal with the darker aspects of it. It could also show how the Naruto world reacts to the presence of someone with such an unusual heritage. There could be new storylines about Naruto facing challenges that are related to his new - found connection to Sephiroth, like dealing with enemies who are either after his power or afraid of what he could become.
In such a fanfiction scenario, Naruto would likely gain some extremely powerful and unique combat skills. Sephiroth is known for his incredible swordsmanship and dark magic - like powers. Naruto might learn new ways to control his chakra, perhaps with a more refined and deadly precision. He could also pick up on Sephiroth's strategic thinking in battle, making him an even more formidable opponent.
Obviously Naruto would be one of the main characters as the title implies he is the son of Sephiroth. Sephiroth himself might also be a major character, perhaps in flashbacks or in some form of influence over Naruto's life. Other Naruto - related characters like Sasuke, Sakura, and Kakashi could also be main characters as they would be involved in Naruto's life and would react to this new revelation about his parentage.
Character growth is also a major theme. As they interact, both Naruto and the female Sephiroth are likely to change. Naruto might learn about the darker side of power from Sephiroth, and Sephiroth could learn about the value of friendship and loyalty from Naruto. This mutual growth makes for an interesting exploration in the fanfictions.
In a fanfic like this, the power dynamic would be very interesting. Sephiroth is a very powerful and intimidating figure. Cloud, as his secretary, would be in a position of both subservience and potential influence. He could use his proximity to Sephiroth to gather information or try to sway some of Sephiroth's more dangerous decisions. It could also create a lot of tension, as Cloud has his own history and grudges, yet he's now in a position where he has to work closely with Sephiroth.
Another great one is 'Female Sephiroth in the Naruto Universe'. This fanfiction takes a different approach. It focuses on how the female Sephiroth adapts to the Naruto universe. She has to deal with the different cultures and powers there. Naruto, being the curious and friendly character he is, tries to help her. It shows a unique dynamic between the two characters.
I haven't read this fanfic specifically. But generally, if Naruto is the son of Sephiroth in this fanfic, it would be a very interesting crossover concept. It might combine the ninja world of Naruto with the unique elements from the world where Sephiroth exists, like different powers and cultures.
Naruto's character would become more serious. Sephiroth's training is no joke and Naruto would have to focus more. He might lose some of his naivete and become more worldly.
One possibility could be that Naruto is drawn to boxing because of its physicality and the determination it requires. He might see it as a new way to test his strength and endurance outside of ninja battles. Maybe he starts training with a local boxing coach who sees his potential and helps him develop his skills.
I'm not sure specifically as I haven't read that exact fanfic. But generally, it might be a story where Naruto, who is in a godlike state, has some sort of connection or interaction with Sephiroth. It could involve Naruto taking on Sephiroth's characteristics or the two of them being in a strange new world together.