Who could be the antagonist in a 'naruto saved by gaara fanfiction'?

The Akatsuki could also be the main antagonists. They are after Jinchuriki, and Naruto and Gaara being together would be a big target for them. They'd likely try all sorts of sneaky tactics to capture them, which would put Naruto and Gaara's friendship and skills to the test.

Well, it could be that Naruto is trapped in a genjutsu and is on the verge of losing his mind. Gaara, with his unique ability to sense Naruto's distress, breaks into the genjutsu world and saves Naruto. After that, they could have a deep conversation about their past and how they've both grown.

It could be Orochimaru. He might manipulate Gaara into kidnapping Sakura. Orochimaru could have his own devious plans for Sakura, like using her medical knowledge for his experiments. So, he uses Gaara's power and his somewhat unstable mental state at times to achieve his goal. Then Sakura and Gaara would have to team up to fight against Orochimaru.

Maybe it's a new villain created specifically for the fanfiction. This villain could have powers that are extremely dangerous to Naruto, like the ability to drain his chakra completely. So the Shinigami has to step in to save Naruto from this new and powerful foe.

Maybe a rogue ninja from Gaara's world who somehow follows him into the DxD highschool. This ninja could have a vendetta against Gaara and use the chaos of the DxD world to try and take him down. They could also team up with some of the devils who dislike Gaara's presence to create more trouble for him.

Another possibility is a group of Death Eaters who have broken away from Voldemort's control and formed their own faction. They see Harry as a symbol of the old regime that they want to overthrow. They target Harry, but his parents, with their knowledge of the old ways and their love for Harry, are able to save him from this group's attacks.

It might be a magical creature that has been corrupted by dark magic. For example, a hippogriff that has been turned evil. It attacks Harry when he's out exploring. Lockhart, who has some knowledge of magical creatures, tries to calm it down at first but when that fails, he has to use more forceful magic to save Harry from the enraged hippogriff.

A group of rogue ninja who are hunting nekoshou for their special powers could be the main antagonists. They see Naruto's newfound connection with the nekoshou as a threat and try to eliminate him and the nekoshou he is protecting.

It could be a corrupt ninja from within the village who wants Naruto out of the way. Maybe someone jealous of Naruto's popularity and power, so they frame him and get him sent to prison. This antagonist would then try to keep Naruto in prison by any means necessary.

Madara Uchiha could be a great antagonist. His powerful Sharingan abilities and his grand plans for the Naruto world would put him at odds with Supergirl. He might see her as a threat to his control and try to manipulate or defeat her. Another option could be Kaguya Otsutsuki. Her god - like powers and desire to reshape the world would clash with Supergirl's values and her attempts to protect the people of the Naruto universe.