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.
To create an engaging Naruto and Hana Hana no Mi fanfiction, start with a strong concept. You could combine a mission in Naruto with the powers of the Hana Hana no Mi. Let's say Naruto and his team have to rescue a hostage, and a new character with the Hana Hana no Mi powers joins them. This character can use their powers to create distractions during the mission, like growing large flower structures to block the enemy's view. Another important aspect is the interaction between the Naruto characters and the new element of the Hana Hana no Mi. Their reactions and how they adapt to this new power can add depth to the story.
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.