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.
The answer to who survived in the end of the second chapter was not clear. The search results did not provide clear information to answer this question.
In the search results provided, there were several recommended harem survival novels. Among them," Kangxi's Harem: The Legend of Concubine Rong " was an ancient harem romance novel that described the heroine's fate and her life in the harem. In addition," Daily Life in the Harem " was also an ancient harem novel that described the life of the female protagonist in the harem. Other than that," The Empress Is Always Unmotivated " and " The Palace Maid's Upper-Ranking " were also some ancient harem novels that were worth recommending. I hope these recommendations can satisfy your needs for harem survival novels.
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.