The " Jin Se " was a long poem by Li Shangyin, a poet of the Tang Dynasty. There was a line in it that read," The Jin Se has fifty strings for no reason, and each string and column miss the year of Hua." This poem was meaningful. It described the fifty strings of the zither, and each string made people miss their lost youth. It expressed the poet's nostalgia and recollection of the past. This poem used the symbolic meaning of the instrument, the zither, to connect the impermanence and changes of life with the beauty of the year, showing the poet's feelings and sorrow for the passage of time.
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.