Well, in a lot of these fanfics, the transformation is a turning point in the story. Before the transformation, Natsu might be facing a seemingly insurmountable challenge. But once he becomes a dragon, he has new abilities to overcome it. His dragon form also often has some sort of connection to an ancient prophecy or power. And as he gets used to his new form, he discovers new aspects of his personality and his past that were hidden before.
A common plot point is the struggle for control. When Natsu transforms into a dragon, he often has to fight to control his new form and its immense power. Another is the reaction of his friends. They are usually shocked at first but then they support him. For example, in many fanfics, Lucy is there to help him understand his new state.
One typical plot point is the origin of the transformation. It could be due to a hidden magic within Natsu that gets triggered. Also, there's often a new enemy or threat that Natsu in his dragon form has to face. In some fanfics, his dragon form attracts other powerful beings, either as allies or enemies. And his relationship with the other dragon slayers might change as he is now more 'dragon' than them.
If you want the clearest chapter reference, go to Chapter 13. Early on, Sensing that something was off with Jiang Yan, Jiang Yan dismissed the...; later, the chapter leans on What on earth do you mean?" Ignoring him once again, Jiang Li shifted her....
Look to Chapter 20 for the clearest answer. It begins with Several people turned their heads upon hearing the sound and saw three..., keeps building through She was clad in a long black dress, and the dull color did not hide her..., and lands on So, he turned and questioned Jiang Li..
The best chapter pointer here is Chapter 47, "This Result Definitely Has Insiders!". It opens with Qi is actually second???] [Did the production team make a mistake? and closes on Qi is so excellent and only got 17, yet Jiang Li comes in with 22?.
Look to Chapter 38 for the clearest answer. It begins with Jiang Li had also observed the girl who had just entered., keeps building through Before arriving, she had briefly reviewed the profiles of the other three..., and lands on He Yun coldly turned his head and continued to maintain his aloof.
Chapter 916, "Not Biological?!", is the clearest early answer because it turns Meng Wanzhi's situation into a concrete plot event. The chapter gives readers a real answer by opening on Bang," Hong Pei slammed the teacup onto the table.
Look to Chapter 84 for the clearest answer. It begins with When the villagers tasted his curry beef one by one, their faces revealed..., keeps building through In the end, he could only secure a score of 5., and lands on Why am I tasting sand in my mouth?" Wen Jiaojiao's bravado gradually....
Chapter 55 is the strongest chapter-level answer because it starts from Su Yinwan hadn't expected that, in just one day, Jiang Li's reputation had... and follows through on He Yun's fans were immediately displeased..
If you want the clearest chapter reference, go to Chapter 15. Early on, Jiang Shixu woke up from those nightmares filled with blood and darkness,...; later, the chapter leans on The two sleeping pills he took in the evening had left him with a....
If you want the clearest chapter reference, go to Chapter 35. Early on, Shining Transformation Trip's filming location was set on the distant...; later, the chapter leans on In order to help the guest stars get better acquainted with one another,....
A practical answer is Chapter 53, because it turns the idea into a concrete scene. The chapter opens with Night had fallen over Chixia Village, eerily void of any human sounds., adds pressure through How does she manage that?] [Now, I really think all the negative press..., and ends on Wait, did.