One possibility is that Igneel would immediately go into a protective mode. He might use his dragon powers to heal Natsu if he has such abilities. Since they have a strong bond, Igneel would be enraged at whatever caused Natsu to get hurt and would seek revenge. He could also stay by Natsu's side until he recovers, providing warmth and comfort as dragons are often associated with being a source of strength and protection.
It could be an enemy dragon. There are many rival dragons in the Fairy Tail universe, and if they see Natsu with Igneel, they might target Natsu to get to Igneel. Dragons can be very territorial and protective of their own, and an enemy dragon may see Natsu as a weak point to attack Igneel through.
One possible reason could be a misunderstanding during a mission. Maybe Erza's actions were misinterpreted by Natsu, leading to him getting hurt, either physically or emotionally.
One great fanfiction could be about Natsu's training with Igneel. In it, Igneel imparts not only fire - based combat skills but also valuable life lessons to Natsu. Another might focus on a time - travel scenario where Natsu goes back in time and meets a younger Igneel, and they form a different kind of bond. There are also fanfictions that explore Igneel's perspective on Natsu's growth as a wizard.
Often, their relationship is depicted as a very strong father - son - like bond. Igneel is seen as the wise and powerful mentor to Natsu, guiding him in his journey to become a great wizard.
One popular storyline is about Natsu's journey to become stronger in the memory of Igneel. He often faces tough battles and overcomes them with the power Igneel instilled in him. Another is where Natsu discovers hidden secrets about Igneel's past that change his perspective on his own life and powers. And sometimes, there are fanfictions that feature Igneel coming back in some form to guide Natsu further in his adventures.
In the fanfiction, Gildarts could meet Natsu and Igneel during a time of crisis. Maybe their town is under attack. Gildarts would immediately jump into action, and Natsu would follow suit, with Igneel guiding Natsu from the side. Gildarts might be impressed by the way Natsu and Igneel work together, as if they share a single mind. They could communicate without words, and Gildarts would try to learn from their unique bond. After the battle, Gildarts would offer to train Natsu further, seeing his great potential enhanced by his connection with Igneel.
Well, one possibility is that Gildarts could share some of his powerful magic techniques with Natsu. Since Gildarts is a very experienced wizard, he might see the potential in Natsu and offer some tips on how to better control his fire magic, which is similar to Igneel's. Maybe he could also tell Natsu some stories about his own adventures that would inspire Natsu to become even stronger.
These fanfictions often show the relationship as a deep, father - son bond. Natsu's love and respect for Igneel are always evident. Some show it through flashbacks of Igneel teaching Natsu important life lessons.