zenitsu using thunder breathing

You need to understand the monsters' behavior. Know when they are most vulnerable and where they are likely to pass by. Then place the thunder traps in those strategic locations.

In fanfiction, Naruto using the Flying Thunder God gives him a strategic advantage. He can set up traps by marking certain areas and then teleporting his enemies into those trapped areas. Also, it allows him to support his allies more effectively. He can teleport to their side in an instant when they are in trouble, like when Sasuke is about to be overwhelmed by an enemy's attack.

No, Zenitsu doesn't die in the manga.

No, Zenitsu doesn't die in the manga. His character survives through the story.

No, Zenitsu doesn't die in the manga.

No, Zenitsu doesn't die in the manga. He survives through the various story arcs.

A simple Nezuko and Zenitsu fanfiction could be that they go on a journey together. Along the way, they encounter other demon slayers who are initially skeptical of Nezuko. But Zenitsu stands up for her, explaining that she's different. This shows the depth of their friendship and how Zenitsu has come to trust Nezuko completely.

One common theme is self - discovery. Since Zenitsu has a complex personality, many fanfics focus on him finding out more about himself, his powers, and his place in the world. Another theme is friendship. He often forms strong bonds with other characters in fanfics, like Tanjiro and Inosuke.

No, Nezuko doesn't marry Zenitsu in the manga.

It's hard to say exactly. The contents of Zenitsu's letter could vary depending on the context and plot of the manga at that point.