In a 'natsu half dragon fanfiction', you could set up a conflict where an evil dragon slayer wants to capture Natsu to use his half - dragon powers for his own evil deeds. Natsu has to fight not only against this slayer but also against his own inner dragon instincts that might be influenced by the slayer's dark magic.
One idea could be exploring Natsu's struggle to control his half - dragon powers. Maybe he accidentally causes destruction in the town and has to deal with the guilt and the fear of others. Another could be a story where Natsu discovers a hidden dragon clan related to his half - dragon heritage and has to prove himself to them.
Perhaps in the fanfiction, when Natsu turns into a dragon, he can communicate with other dragons in a way he couldn't before. This could lead to him uncovering secrets about his past and the origin of dragons in that fictional world. He might find out he has a special destiny related to the dragons.
In some fanfictions, Natsu might have different dragon slayer magic elements. Instead of just fire, he could have a combination of fire and lightning, which would make his attacks even more powerful and unique. Also, there could be stories where Natsu travels to different dimensions or time periods, which would introduce all kinds of new challenges and adventures for him. This could lead to him meeting alternate versions of his friends or even new characters.
One idea could be that Hiccup discovers a new type of half - dragon that has unique abilities, like the power to control time briefly. This could lead to adventures where he has to use this new discovery to save Berk from an ancient threat that is about to be unleashed. Another plot could involve the half - dragon being a hybrid of a very rare and powerful dragon species, and Hiccup has to protect it from dragon hunters who want to use its power for evil.
In this fanfiction, perhaps Harry's connection to the dragon side would change his relationship with other magical creatures. He could have a special bond with dragons, understanding them on a deeper level. This could lead to him being involved in dragon conservation or training in a way that normal wizards aren't. Also, his appearance might be slightly altered, with some dragon - like features that make him stand out even more at Hogwarts.
One common theme is self - discovery. Since Natsu is a half - dragon, he often has to figure out what that means for him. He may discover new powers or abilities that come with his dragon heritage. Another theme is acceptance. He has to deal with how his friends and the guild will accept his new identity. For example, will they be afraid of him? Or will they see it as just another part of who he is? And power struggle is also a theme. Natsu may have to learn to control his new - found dragon powers, and there might be forces that want to either use him or stop him because of his half - dragon status.
One idea could be that Natsu discovers unique magical abilities passed down from the Dragon God that set him apart from other mages. For example, he might be able to communicate with all types of dragons, not just the ones he's related to in the original story.
One idea could be Natsu exploring a new magic ability related to his dual dragon slayer powers. For example, he discovers a way to combine the fire of his Igneel - taught magic with the other dragon's element in a more powerful and unique way.
Well, a cool plot might involve Natsu being transported to a parallel world where he is the only water dragon slayer. He has to adapt quickly to this new role and use his skills to fight against an evil force that is draining the water from that world. Also, he could meet alternate versions of his friends and have to convince them to trust him, since his powers are so different from what they know.
Another plot could involve Natsu turning into a dragon in a completely different world. He has to adapt to this new world as a dragon and find a way to turn back. Along the way, he meets other dragons who teach him about his new form and its capabilities. This could lead to him having a greater understanding of his own powers when he finally returns to his normal self.
One plot idea could be that Natsu discovers a new, hidden power within his Alph Dragon Slayer abilities. Maybe he can communicate with ancient dragons that were previously unknown. Another idea is that he has to compete in a tournament against other dragon slayers with unique powers. This would lead to intense battles and character development.