Well, first of all, the element of novelty. Izuku being the youngest pro hero is not a common concept in the original story, so in the fanfiction, it brings a fresh perspective. His inexperience also leads to some comical and heart - warming moments as he learns on the job. Additionally, his interactions with the hero community at large, from the big - name heroes to the side - characters, are key elements that shape the story and his journey as the youngest pro hero.
Sure. One popular 'izuku youngest pro hero fanfiction' might be 'Izuku: The Youngest Pro Hero's Ascent'. In this fic, Izuku overcomes numerous challenges at a very young age to become a pro hero. It's full of action and character development.
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.