The voice of a story in English usually refers to the style or tone in which the story is told. It could be serious, humorous, or something in between.
I would recommend 'The Adventures of Sherlock Holmes'. The stories are full of mystery and intrigue. The characters are vividly described, and the plot twists keep you hooked. The English voice for this, if you can find a good audiobook version, really brings the Victorian London setting to life.
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.