One reason could be that he has deep feelings for her. He might not be used to having such strong emotions for someone and this possessiveness is his way of showing how much he cares.
Perhaps he sees something special in fem Naruto that he doesn't want to share with others. Maybe it's her kindness or her strength. He feels that she's unique and he doesn't want anyone else to have what he has with her. Also, he might have a sense of competition with other characters in the Naruto world who might also be interested in fem Naruto, which makes him more possessive.
In this fanfiction, Gaara's possessiveness could be demonstrated in different ways. Firstly, he might be possessive in terms of her time. He wants to spend as much time as possible with her. Secondly, he could be possessive about her emotions. He doesn't want her to be too friendly with other guys as he fears she might develop feelings for them. Also, he may be possessive about her safety, always being on guard and ready to fight off any threats to her.
One possible reason could be a deep emotional bond. Maybe Gaara has seen Naruto's unique strength and kindness, which makes her feel a strong connection. It could also be due to a sense of protection. Naruto might have been in situations where he was vulnerable, and Gaara's possessiveness is her way of ensuring his safety.
Naruto might be initially confused. He is used to being friendly with everyone, and this sudden possessiveness from Fem Gaara could catch him off - guard. So he may just try to talk to her to understand why she is acting this way.
One reason could be friendship. Gaara and Naruto have a special connection in the original story. In fanfiction, this connection could be deepened, and Gaara would save Naruto because he values their friendship. Just like Naruto once reached out to Gaara, Gaara would do the same for Naruto when he's in danger.
One reason could be that she lost so much time with Naruto due to her early death in the original story. So in the fanfiction, she's overcompensating for that lost time by being possessive.
One reason could be that Gaara, being a powerful and complex character, might have a different view on the concept of friendship. If he were to tell Naruto that his friends are only with him out of obligation or because of his status as a hero, Naruto might start to doubt his relationships and become depressed.
Yes, there are likely fanfictions out there with this concept. The Naruto fandom is quite large and diverse, and many fans like to explore different pairings in their fan - created stories. This particular pairing might attract those who are interested in seeing a different dynamic between Naruto (in a female version) and Gaara.
A possible plot could be that both fem Naruto and Gaara are forced into an arranged marriage by their villages to strengthen the alliance. At first, they are reluctant, but as they get to know each other better, they find common ground. Fem Naruto might teach Gaara more about friendship and love, while Gaara helps fem Naruto understand the harshness of the desert life. As they overcome difficulties together, their relationship deepens into a loving and committed mate - ship.
Fanfiction in this area often delves into the psychological aspects of the characters. Since Naruto and Gaara both have complex pasts, a female Naruto can bring new angles to their interactions. For example, she might be more empathetic towards Gaara's childhood traumas, leading to deeper conversations and a stronger bond between them.
One reason is their friendship. Naruto was one of the first people to see Gaara as a person, not a monster. So, Gaara would feel indebted to Naruto and be willing to risk his life. Another reason could be for the sake of the ninja world. Naruto is often seen as a key figure in maintaining peace, and Gaara, as a responsible leader, would understand the importance of saving him.