In this type of fanfiction, the character development of Sakura would be really interesting. She would likely have to go through a huge transformation from a regular character to one capable of such a heinous act. It could also show how the other characters in the original story react to her actions. For instance, her friends might be in disbelief or try to stop her.
Well, perhaps the plot could start with Sakura uncovering some dark secrets about her clan. These secrets could be something like her clan being involved in illegal or immoral activities, which makes her feel that she has to take drastic measures to stop them.
One possible motive could be revenge. Maybe Naruto was led to believe that the Namikaze clan was responsible for something terrible that happened to him or someone he cared about. Another motive could be power. If there was some sort of power within the clan that Naruto thought he could gain by eliminating them.
Perhaps in the fanfiction, Naruto is tricked into believing his clan is a threat to the village. So, in an attempt to protect Konoha, he takes drastic measures and kills them. It could also be that a powerful and evil entity takes over Naruto's body, and using his strength, murders the clan while Naruto is powerless to stop it from within.
Yes, it is a very dark twist. In the original Naruto story, Naruto is a part of the Uzumaki clan, and the Namikaze clan is his father's clan. Having Naruto kill the Namikaze clan goes completely against the established relationships and values in the original series. It's a concept that challenges the idea of family and loyalty that is so central to the Naruto universe.
It could be a situation where Naruto discovers some dark secret about the Uchiha clan that he believes makes them a danger to everyone. For instance, if he found out they were planning a coup that would involve mass destruction, he might think that killing them was the only way to save the village and the rest of the ninja world.
Well, in this fanfiction scenario where Naruto kills the Uchiha clan, it would mean the end of the Sharingan bloodline in a very unexpected way. This would have huge implications for the ninja world. Without the Uchiha, there would be no potential for the Mangekyou Sharingan or the Eternal Mangekyou Sharingan. The balance of power in the ninja world might shift as the Uchiha were quite powerful. And Naruto himself would be a very different character. He's always been about protecting and saving people, so this act would make him a much darker and more complex figure, almost an anti - hero.
Maki in fanfiction usually has a fierce loyalty to her friends, especially Yuta. She is the type to fight for what she believes in. Yuta is sometimes portrayed as being a bit naive in the ways of the world outside his own small circle, but his pure heart makes him endearing. In many stories, their different personalities create an interesting dynamic, like in a story where Maki's boldness gets them into a risky situation and Yuta's calm thinking gets them out.