zenitsu turns into demon

No, Zenitsu doesn't die in the Demon Slayer manga.

My knowledge doesn't have anything related to the main character becoming a demon king. Can you provide me with more relevant information so that I can better answer your questions?

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.