Well, it could be that in this fanfiction, Naruto has some sort of hidden agenda. He might call Sakura ugly as a form of reverse psychology. He could be thinking that by doing so, she'll prove him wrong and become more confident. Or perhaps there's some miscommunication or misunderstanding between them. For example, Naruto misheard someone talking about Sakura in a negative way regarding her looks and he wrongly believes it, so he says she's ugly.
One great thing about Sai and Sakura fanfiction is the creativity. Some stories might have them in alternate universes, like a modern - day setting where they are ordinary people. In these, Sai could be an artist and Sakura a doctor, and their paths cross in a new and exciting way.
Fanfiction about Sai and Sakura can be really interesting. It allows fans to explore different relationships and scenarios that might not have been fully explored in the original series. For example, some fanfictions might focus on their friendship, how Sai, with his unique personality, interacts with Sakura, who is strong - willed and kind. Writers can create stories where they go on adventures together, or face challenges within the ninja world that test their bond.
He could also get angry. After all, being misjudged like that is unfair. His anger could lead him to either lash out verbally at Sakura or he could leave the village in a fit of rage, feeling that he is not accepted even by his friends. This could then lead to a series of events where Naruto has to find his own way and Sakura realizes her mistake later on.
Maybe they time - travel to a time when a great war was about to start. Sakura, with her medical skills, and Sai, with his strategic thinking from being an Anbu, could work together to prevent the war. They could try to change the minds of the leaders involved by showing them the future consequences of the war. This would involve a lot of sneaking around and trying not to be discovered as time - travelers.
One common theme is friendship. Despite their different personalities and pasts, the stories often focus on how they can become friends. For example, Sai has his own past traumas and unique way of interacting, and the fanfics may show how Sakura and Sasuke gradually accept him into their circle.
One common theme is the discovery of love. Since Sai has a rather unique personality, it's often about Sakura getting to know him better and realizing her feelings for him.
One popular sai sakura fanfic might be about their adventures together in a magical world. For example, they could be on a quest to save their village from an evil sorcerer. In this fanfic, Sai could use his unique abilities and Sakura her medical ninjutsu and combat skills to overcome various obstacles.
Archive of Our Own (AO3) is also a great place. It has a well - organized tagging system. Look for the 'Naruto' tag first and then narrow it down to 'Sai Sakura' related works. There are often some high - quality and unique fanfics there.