Definitely not ethical. The Naruto world is rich with different cultures and characters, and reducing a character like Hana to a slave in fanfiction is inappropriate. It not only violates the spirit of the original work but also can create a negative and uncomfortable reading experience for others.
It could have a negative impact. It might make some fans uncomfortable or even angry as it goes against the positive nature of the Naruto series. Many fans love the show for its themes of hope and camaraderie, and this type of fanfiction would be a deviation from that.
Well, it could be a story where Hana is somehow magically bound to serve Naruto. Maybe she owes him a great debt and has to be his slave as a result. This could lead to various adventures where Naruto has to protect Hana while she's in this subservient role.
Maybe the main antagonist is a dark sorcerer. The sorcerer's goal could be to use Hana's enslavement to Naruto to corrupt Naruto's positive energy. They might believe that by forcing this strange relationship on them, they can turn Naruto towards the dark side. So this sorcerer would constantly try to create more problems between Hana and Naruto.
It's also possible that Hana is related to one of Naruto's friends. Maybe she's Kiba's sister or something. And because of her connection to Naruto's friend, Naruto feels responsible for her safety. So when she's in trouble, Naruto steps in to save her without hesitation.
Hana could be an original character created for this fanfiction. Maybe she is a new ninja in the village who Naruto falls for, but she has a hidden agenda that ends up breaking his heart.
In a fanfiction, Naruto could befriend Hana and Tsume in a different context than in the original series. For example, they might meet during a training session in a hidden forest. Their different personalities would create interesting dynamics. Naruto's optimism, Hana's calmness, and Tsume's intensity would all play a role in how they interact.
One possible fanfiction could be about Naruto, Hana, and Tsume teaming up on a mission. Maybe they have to protect a hidden village from a new threat. Naruto's strength, Hana's skills with animals, and Tsume's fierce combat abilities could make for an exciting story.
One possible fanfiction could be about Naruto going on a mission with Tsume and Hana. They might encounter a powerful enemy in the forest. Naruto could use his shadow clone jutsu to distract the foe while Tsume and Hana attack from the sides. This would showcase their teamwork and different fighting styles.