One possible plot could be that Issei discovers a hidden power within himself that gradually transforms him into a dragon. This new form gives him enhanced strength and abilities, but also attracts the attention of powerful enemies who want to either control him or eliminate him. He has to learn to master his dragon form while also protecting his friends and loved ones.
In a fanfiction about Issei turning into a dragon, perhaps it starts with an ancient curse that was placed on his family line long ago. As he reaches a certain age or experiences a specific event, the curse begins to take effect. His transformation into a dragon could be a painful process that he initially struggles to accept. However, with the help of his friends, he comes to terms with it and uses his new dragon powers to fight against the forces of evil that are plaguing his world. He might also gain the ability to fly and breathe fire, which would be really cool.
The fanfiction could revolve around Issei being experimented on by a secret organization. They inject him with a serum made from dragon DNA, which slowly starts to change his genetic makeup. As he turns into a dragon, he not only has to deal with the physical changes but also the mental ones. His instincts become more primal, and he has to fight to keep his humanity. Meanwhile, he discovers that there are other dragon - like beings out there, some friendly and some not, and he has to navigate this new world of dragons while trying to find a way to reverse the transformation if he so desires.
Well, it could involve Issei discovering some ancient dragon magic. Maybe he stumbles upon a dragon's lair and is blessed with dragon powers. He might start to have dragon - like instincts, like a strong urge to hoard treasures or protect a certain territory.
One possible plot could be that Astrid is cursed by an evil sorcerer. At first, she has no idea what's happening to her but slowly starts to notice physical changes like her skin getting scaly. As she turns more and more into a dragon, she has to struggle to maintain her relationships with her friends who are initially afraid of her new form. Eventually, she discovers a way to break the curse through an ancient magic ritual.
One possible plot could be that Eragon, while facing a powerful dark enemy, discovers a hidden ancient magic that causes him to transform into a dragon. As a dragon, he has to quickly adapt to his new form, learning to fly and use his newfound dragon abilities like enhanced strength and fire - breathing. He then uses these powers to defeat the enemy and protect his land.
Maybe in the fanfiction, Natsu's emotional state causes him to turn into a dragon. After a great loss or a fit of extreme rage, his magic reacts and he transforms. This new form is both a blessing and a curse. It gives him the power to protect his loved ones better but also isolates him as he struggles to understand and control his new dragon instincts.
One possible plot could be that Harry is under a powerful dark spell. The transformation into a dragon might be a part of a scheme by Voldemort or his followers to either discredit Harry or use his new form for some evil purpose. Maybe Harry has to learn to control his dragon form in order to fight back and protect Hogwarts and his friends.
One possible plot could be that Hiccup's transformation into a baby dragon is the result of a magic spell gone wrong. He then has to figure out how to reverse it while experiencing the world from a dragon's perspective. He might make new dragon friends who help him understand his new form and search for a cure.
In a fanfiction where Issei turns into a dragon, his relationships would be in flux. His relationship with his mentors or those he looks up to might change as they now see him as a different kind of being. They might treat him with more caution or more respect depending on how they view dragons. His friendships with his peers would also be altered. Some might see him as a weapon to be used in their battles or struggles, while others would see him as a friend in need of support. Romantically, if he had feelings for someone, that person would have to deal with the fact that Issei is no longer fully human. There could be jealousy from others who might want to be with the powerful dragon - Issei, or there could be newfound admiration from those who previously overlooked him.
Well, it could be about Issei Hyoudou ascending to become a Dragon God. Maybe he discovers some ancient power within himself that is related to the Dragon Gods. He might have to face various challenges and enemies who are either afraid of his new - found power or want to use it for their own purposes.
In the fanfic, Astrid could be part of a scientific experiment gone wrong. The experiment was meant to study dragon DNA, but something malfunctioned and she starts to transform. She then embarks on a journey to find a cure. Along the way, she discovers that being a dragon gives her a unique perspective on the world and she has to decide if she really wants to go back to being fully human.
The plot could start with Cell having a change of heart after a near - death experience. Maybe he realizes the futility of destruction. Then he could start to learn about the values of the Z - fighters and try to fit in with them, while also using his powers for positive things like helping to train the younger fighters.