One idea could be a fanfic where a young ninja discovers a unique way to combine lightning jutsu with other elements like water, creating a new and powerful technique. This could lead to him being sought after by different clans for his knowledge.
In Naruto fanfiction, cheat codes can drastically change the use of jutsu. They might allow a character to instantly master a jutsu that usually takes years of training. For example, a cheat code could give Naruto the ability to use the Rasengan without any training from Jiraiya. It's a fun concept that adds an interesting twist to the Naruto universe.
In fanfiction, the reanimation jutsu might have extended or modified limitations. For instance, in the original, there were clear rules about the caster's control over the reanimated. But in fanfiction, a writer could create a scenario where the reanimated can break free of that control more easily. Also, the source of the sacrifice for the jutsu could be different. In the series, it was usually human sacrifices, but fanfiction might explore using other forms of energy or substances.
Maybe he found some hidden scrolls left by his mother. These scrolls could have contained the details of her jutsu. Naruto, being the curious and determined ninja he is, would have studied these scrolls carefully and learned the jutsu.
A third idea for a Naruto poison jutsu fanfic could be a story set in a different era of the Naruto universe. In this time, poison jutsu is a highly respected and feared art. A young ninja, inspired by tales of Naruto, tries to master poison jutsu. However, they face many challenges, including a corrupt master who wants to use the ninja's skills for evil. The young ninja must then decide whether to follow the master or break away and use their skills for the greater good.
A fanfic could also explore Naruto using the Smoke Jutsu for a rescue mission. Suppose some of his friends are trapped in a building surrounded by enemies. Naruto uses the Smoke Jutsu to cover the area. The smoke is so thick that the enemies can't see. Then he sneaks into the building, rescues his friends, and they all escape under the cover of the remaining smoke.
Well, it could be the Uzumaki Chain jutsu. In the Naruto lore, the Uzumaki clan had some unique abilities and the chain jutsu was one of them. His mother Kushina was from the Uzumaki clan, so it's possible that's the jutsu he learned in the fanfiction.
One common theme is the discovery of new sealing jutsu. Writers often create new and powerful sealing techniques for their characters to find or develop. Another theme is the power struggle related to sealing jutsu. Since they can be used to seal away great power or even demons, there's often a fight over who controls them.
First, do research on all the existing lightning jutsu in Naruto. This will give you a solid base for your fanfic. Then, create unique characters with their own relationships to lightning jutsu. For example, a character who fears lightning but has to learn lightning jutsu to protect their loved ones.