In some fanfictions, Snape has badass moments when he outsmarts Voldemort. For example, he manages to mislead Voldemort about the location of a crucial magical artifact. He uses his Occlumency skills to his advantage, hiding his true thoughts and intentions while presenting false information in a very clever way. This not only shows his intelligence but also his courage as he risks his life to deceive the Dark Lord.
There could be a moment where Percy stands up to an unjust authority figure in the fanfiction world. He defies them with such confidence and charisma that it makes him seem like a total badass. Or perhaps he dives into a dangerous, unknown realm to save someone, showing his fearless and selfless side which is very badass.
One possible badass moment could be when bella stands up to a powerful alpha wolf. She shows no fear and uses her sharp tongue to put the wolf in its place.
One badass moment could be when Ezra single - handedly takes on a group of stormtroopers in a narrow corridor. Using his lightsaber and the Force to deflect blaster bolts back at them, he cuts through their ranks like a hot knife through butter. Another might be when he uses his Force powers to manipulate a large ship's controls from a distance to prevent it from crashing into a rebel base.
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.