Rock Lee could be an excellent third character. His positive attitude and unique fighting style would contrast well with Gaara and Naruto. He could bring a lot of energy and humor to the story, and his loyalty and determination could be a great addition to the triad's dynamic.
Sasuke would be a great choice. His complex relationship with Naruto and his own history with Gaara make for a lot of potential drama and interesting character interactions. There's so much history between the three of them that can be explored in different ways.
One plot idea could be a story where Gaara, Naruto, and a third character, say Sasuke, are on a mission together to protect a hidden village from a new and powerful enemy. They have to learn to combine their unique skills and overcome their differences to succeed.
It could be Orochimaru. He's always been after Naruto for his special powers. He might set a trap for Naruto, but Gaara intervenes and saves him. Orochimaru's motives of immortality and his dark jutsu make him a great antagonist for this kind of story.
Sirius Black is an excellent choice. His rebellious nature and his connection to Harry can bring in some interesting storylines. He could be like a mentor to the triad, especially when it comes to dealing with the darker aspects of the wizarding world. Neville Longbottom can also be included. He has his own growth arc in the original series, and in a triad fanfiction, he could be a source of support and strength, especially when they are all facing challenges in Hogwarts.
One great 'Naruto Gaara fanfiction' story is 'The Redemption of Gaara'. It shows Gaara's journey towards finding inner peace after all his hardships. Another is 'Gaara's New Path' which focuses on his growth as a leader in Suna. And 'Gaara and Naruto: Unlikely Bond' is also interesting as it delves into their unique friendship in a creative way.
One great author in Naruto, Neji and Gaara fanfiction is KiraK. They have a really good grasp on the characters' personalities and write engaging stories. Another is NovaScribe. Their stories often have unique plot twists that keep you hooked. And then there's FlameWriter. They are known for their detailed descriptions of the ninja world in their fanfictions.
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.
Rock Lee could be an interesting main character for a Third Shinobi War fanfiction. Since he doesn't rely on ninjutsu, his unique fighting style could be a great asset during the war. We could see him face off against powerful ninjutsu users from other villages and prove that taijutsu is just as effective. Also, his unwavering determination could inspire his comrades during the dark times of the war.
One great 'Naruto Fuu and Gaara' fanfiction is 'The Bond Beyond Nations'. It focuses on how Fuu and Gaara's relationship develops over time, with Fuu being a character who initially misunderstands Gaara but then comes to see his true self. It has a lot of well - written emotional moments.
I really like 'A New Alliance'. In this fanfiction, Naruto, Gaara, and Sasuke are forced to team up against a new and powerful enemy. The author does a great job of portraying their individual strengths and how they complement each other. It's full of action and has some interesting character development for all three.
There's also 'Naruto and Gaara: Allies for Eternity'. In this story, they face a new and powerful enemy together. The story is well - written as it shows the unique skills of both characters and how their combined strength is much greater. It also has a lot of emotional moments that make it a great read.