The relationship with Ladybug would be different too. If Adrien is in Gabriel's body, his interactions with Ladybug would be based on his new identity. Ladybug might be suspicious of this 'new' Gabriel. And Gabriel as Adrien might try to use his knowledge from his original self to either help or hinder Ladybug in a different way than the real Adrien would. Also, the friendships at school would be affected. Adrien's friends would notice a big change in 'Adrien' (Gabriel) and might not understand what's going on.
The father - son relationship would be completely turned on its head. Instead of Gabriel being the strict and often distant father, Adrien would be in that role. He might be more understanding and lenient towards himself (in Gabriel's body). And Gabriel, as Adrien, would have to deal with a father - like figure in Adrien's real father. This would create a very strange and new dynamic between them.
Well, perhaps a plot point could be the reactions of the Kwamis. When Adrien and Gabriel swap, the Kwamis that are used to one person's personality and way of doing things would have to adjust. For example, Plagg might be really confused with Gabriel in Adrien's body. Also, the way they use the Miraculous powers could change. Adrien might use the powers in a more positive and heroic way compared to Gabriel's more self - centered motives in the original role.
This event in the fanfic could also lead to new characters emerging. Maybe someone would try to take on Ladybug's mantle in a different way. Or new villains could rise, seeing the opportunity in the chaos. The magic of the Miraculous might be affected too. Since Ladybug was an important part of the magical balance, her death could have unforeseen consequences on the powers and the Miraculous themselves.
His character could become more withdrawn. Normally, Adrien is charming and outgoing, but drugs in a fanfic might make him isolate himself from others as he gets caught up in this new and dangerous world.
Adrien could develop a darker side. The Peacock Miraculous has some negative connotations in the show. If he uses it, he might be influenced by its more shadowy aspects. He could become more secretive and withdrawn as he struggles with the power and the potential harm it could cause.
His character would likely become more complex. With the power of the Butterfly Miraculous, Adrien would have to grapple with the moral implications of using such a powerful and potentially dangerous item. He might become more cautious and less impulsive as he realizes the consequences of his actions.
The dynamic between Poseidon and his son, Percy (in the original), would be completely flipped. Instead of a father - son relationship, they would be more like two separate entities with Poseidon now in Percy's role. Poseidon would have to face the same challenges Percy did, but without the advantage of Percy's unique experiences as a demigod growing up.
If the kwami swap involves a kwami with a mischievous nature, Lady Noir's personality could become more playful. She might start cracking more jokes during battles, much like Chat Noir usually does. This would change her overall demeanor and how she interacts with both the villains and Chat Noir. It could also make their partnership more light - hearted or, if Chat Noir isn't used to it, a bit more chaotic as they adjust to this new side of Lady Noir.
He could become more self - reflective. After the rejection, Adrien would likely take time to think about what went wrong and what he could do differently. This might lead to him becoming more mature in his approach to relationships.
The character dynamics would change significantly. Other characters who were close to Oz, like Glynda, would have to adjust to the new 'Oz' (the reincarnated 'Si'). They might sense that something is different about this Oz. The relationships with the main characters, like Ruby, Weiss, Blake, and Yang, would also be different. This new Oz might have a different approach to mentoring them or guiding them in their fight against the Grimm.
The character dynamics would change a lot. For example, Iron Man might see Spider - Man as a protege in this fanfiction. He could be more protective and try to mentor Spider - Man. Meanwhile, Thor might find Spider - Man's small - scale heroics amusing compared to his own grand battles. Hulk could be a bit unpredictable around Spider - Man, either scaring him or having an odd friendship develop.