Perhaps they get left back because of some external factors. Say, an enemy attacked their guild right before an important exam. Lisanna and Natsu were so busy fighting off the enemy and protecting their guildmates that they missed out on crucial study time. They might have also gotten injured during the battle, which further hindered their performance in the assessment, causing them to be held back.
Their relationship with the guild leaders could become strained. The leaders might see them as irresponsible for getting left back. However, as time passes, Lisanna and Natsu could prove themselves in other ways, like taking on extra tasks around the guild to show their dedication. This could gradually change the leaders' perception of them and strengthen their relationship in the long run.
The main characters are clearly Natsu and Lisanna. Natsu is a well - known character with his fiery personality and powerful dragon - slayer magic. Lisanna is also important, she has her own set of skills and a unique relationship with Natsu.
In this kind of fanfiction, they might face various challenges. Maybe they'll have to find their way back on their own. They could encounter dangerous magical creatures and have to rely on their own skills and the bond between them to survive.
One popular storyline is where Natsu and Lisanna go on an adventure together to find a long - lost magical artifact. This adventure tests their relationship and their individual strengths. Another is a story where they have to team up to save the Fairy Tail guild from a powerful enemy. It often involves them using their unique magic skills in creative ways.
A plot could be that Natsu and Lisanna have been longing for a baby. They go through a magical ritual in their guild to increase their chances of having a child. Once Lisanna becomes pregnant, the whole guild gets involved. Everyone is excited and offers their help. Natsu becomes super protective of Lisanna and the unborn baby. There could be a sub - plot where an enemy tries to target Lisanna because of the powerful baby she is carrying, and Natsu has to fight to keep them safe.
Another idea in fanfiction could be a 'what if' scenario. What if Lisanna never 'died'? In this case, their love could have blossomed earlier. They might have been a couple throughout the main series, and fanfictions could explore how that would have changed the dynamics between Natsu and the other characters like Lucy.
Love is a very common theme. Since they have a pre - existing relationship in the original story, fanfictions often expand on their romantic feelings for each other. Another common theme is friendship. Their friendship is the foundation of their relationship, and many fanfictions explore how their friendship evolves into something more.
Lisanna might face a lot of backlash from the guild. Her friends could be disappointed in her and might not trust her as much. She could lose her standing in the guild and have to work hard to regain people's respect.
A plot point could be the couple's journey to find the perfect wedding venue. They might explore different magical places in the Fairy Tail world, like a floating castle or a hidden valley. Then there's the issue of the wedding dress. Lisanna could have a hard time choosing one, with all her friends giving different opinions. In the meantime, Natsu could be training to become a better husband, learning how to cook and do household chores with the help of some of the other guild members. And finally, the actual wedding day could be filled with unforeseen events, like a sudden storm that they have to magically overcome to have the perfect ceremony.
Well, in many fanfictions, Natsu might initially be in shock. He's a passionate character, so he could react with anger. He might lash out at Lisanna or the person she cheated with. He could also go into a state of self - doubt, wondering what he did wrong.