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.
I'm not entirely sure which specific 'Wonder Woman Ryona Stories' are popular as it's not a very common mainstream concept. However, some might involve her facing powerful adversaries in unique and challenging battles where she showcases her strength and determination.
Typically, the 'Ryona' concept often involves a certain level of combat intensity that might not be entirely suitable for very young kids. However, if there are stories that tone down the more extreme aspects of Ryona and focus more on Wonder Woman's positive values like courage and justice, they could potentially be made kid - friendly.
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.