I haven't actually read this fanfiction, so I can't summarize it directly. But generally, it might involve Deadpool taking on the role of an adoptive figure to a young Peter. There could be humorous and action - filled situations as Deadpool's chaotic nature meets Peter's youthful exuberance and potential powers.
Nezuko is initially 12 years old in the manga. As the story unfolds, her age doesn't change significantly in a traditional sense, but her character development is quite remarkable.
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.