Perhaps Gaara was under a dark influence or had a mental breakdown. The result could be a loss of trust from others and a struggle for his own redemption. It might even set off a chain of conflicts within the village that he has to face and overcome.
Maybe Gaara was driven by deep-seated anger and trauma. The consequence could be a total change in his relationship with Sakura and his place in the community.
Perhaps the plot could involve a misunderstanding. Gaara is sent to capture or subdue Sakura because she's suspected of something she didn't do. Sakura, of course, won't go down without a fight. She tries to reason with Gaara at first, but when that fails, she attacks. The fanfic could then explore how they gradually learn the truth during the fight. Gaara might start to respect Sakura's tenacity and Sakura might understand Gaara's loyalty to his village better.
For Sakura, she might become more confident in her combat abilities. Working with Gaara, who has such strong and intimidating power, could push her to step up her game. She could also develop more empathy as she gets to know Gaara's troubled past. For Gaara, he could start to open up more to others. Sakura's kindness and determination might make him realize that not everyone is out to harm him.
Maybe in the fanfiction, Sakura, being a medical ninja, is sent to Suna to help with some sort of epidemic. There she meets Gaara. Gaara is intrigued by her skills and determination. As she heals the sick in Suna, Gaara offers his protection. During this time, they share stories about their pasts, like Sakura's relationship with Sasuke and Gaara's own troubled childhood. This sharing brings them closer together and a bond starts to form between them.
Another plot could be a misunderstanding. Gaara might misinterpret Sakura's actions as a threat to his village or to someone he cares about. His over - protectiveness then leads him to lash out at Sakura. He may not realize until later that he has hurt her deeply, both in terms of her body if there was a physical altercation and her feelings.
One possible story could be that Sakura goes to the Sand Village for a medical mission while Gaara is Kazekage. They start to interact more, and Gaara is impressed by Sakura's strength and kindness. Eventually, they form a strong friendship that helps in strengthening the bond between the Leaf and Sand villages.
One possible motive could be a complete breakdown of the peace they had worked so hard to build. Maybe an outside force manipulates Gaara's mind, causing him to turn on Naruto. Another could be extreme jealousy over Naruto's popularity or power.
One possible plot could be that Gaara, the quiet and brooding type, and Sakura, the strong - willed girl, are paired for a school project in highschool. At first, they clash because of their different personalities. Gaara is reserved and Sakura is more outspoken. But as they work together, they start to understand each other better. Sakura realizes that Gaara has a kind heart beneath his cold exterior, and Gaara sees Sakura's determination and compassion. Eventually, they become good friends and maybe even develop a deeper connection as they face challenges together in highschool, like dealing with bullies or difficult exams.
One possible plot could be that Gaara, initially cold and reserved, starts to develop an intense, possessive feeling towards Sakura. Maybe he sees her kindness and determination during a mission and becomes fixated on protecting her in his own possessive way. This could lead to conflict with Sakura's friends who don't understand his motives at first.
One possible plot could be that Gaara discovers a new type of jutsu that allows him to fly and he decides to teach Sakura. As they practice together, they bond over their shared experience and overcome their individual insecurities. They then use their new flying ability to explore new areas and encounter various challenges along the way.
I'm not sure specifically as I haven't read that exact fanfic. But it could potentially be a story where Sakura endures some form of abuse within the context of a relationship or situation involving Gaara. However, this is just speculation without reading the actual piece.