One common theme is the overcoming of Gaara's past traumas in the context of a relationship with Matsuri. Another is Matsuri's support for Gaara as he takes on his role as Kazekage. Also, the idea of them finding solace in each other in a world full of shinobi battles is quite prevalent.
Well, a frequent theme is the growth of their relationship. It often starts with Matsuri's long - standing admiration for Gaara. Then, as they interact more, they start to understand each other on a deeper level. And of course, there's the theme of loyalty. Matsuri is loyal to Gaara and their relationship in the fanfictions, and Gaara learns to trust and love her in return. There's also the theme of protection, with both characters being shinobi, they often protect each other in the stories.
Common themes include the exploration of Gaara's emotional journey with Matsuri by his side. Since Gaara had a difficult past, having Matsuri as a loving partner helps him open up more. Also, the theme of cultural differences within the Sand Village can be explored, as their relationship may bridge certain gaps. Another theme could be the power couple aspect, as they both are strong shinobi and their combined strength can be a significant part of the story, along with their love for each other.