A common theme is friendship. Since they are part of the Fairy Tail family, fanfictions often focus on how Nashi and Storm support each other through tough times, like when the guild is under attack or they are on a difficult mission.
Another theme could be family legacy. Given that they are likely to be the children of well - known Fairy Tail members, fanfictions may explore how they live up to or break away from their parents' reputations. They might feel pressured to be as strong or as heroic as their parents, and the story could revolve around how they deal with that pressure.
Adventure is also a big theme. Writers like to send Nashi and Storm on exciting quests, exploring new lands, and facing unknown magic and creatures. It's a way to show their growth as characters and their ability to overcome challenges. For instance, they might journey to a far - off island to find a rare magical item.