One interesting fanfiction could be one where Viserys Targaryen manages to escape his fateful end in the series. He might gather allies in Essos and build an army strong enough to actually take back the Iron Throne. This would show a different side of his character, more of a survivor and a strategic thinker rather than the impulsive and cruel figure we saw in the show.
In certain fanfictions, Viserys could be shown as a tragic figure. His pride and his sense of entitlement are still there, but his downfall is explored in more depth. He might be portrayed as a man who was in over his head, trying to play a game of thrones that he didn't fully understand, and his personality flaws are what ultimately led to his demise.
Aegon Targaryen and the Mad King (Aeris Targaryen II) were father and son. Aegon Targaryen was the son and only son of Rhaegar Targaryen and Eliya Martell. Mad King Aerys Targaryen was Aegon Targaryen's father.
One possible plot could be about the rise of the OC (original character) as a Targaryen king. Maybe he has to fight off rival claimants to the throne, using his unique skills and the power of his dragons. He could also be involved in political intrigue within the Seven Kingdoms, making alliances and enemies as he tries to establish his rule.
Tyrion Lannister is often a popular character in these fanfictions. His intelligence and complex personality can add a lot to the story. He might befriend Daenerys or even be a mediator between her and Viserys in some alternate universes.
Obviously, the main character would be the 18th Targaryen king OC himself. He would be the central figure around which the story revolves. His advisors could also be important characters. Maybe an old, wise maester who has been in the court for years and tries to guide the young king. And of course, his enemies, like a power - hungry lord who wants to usurp the throne.
A fanfiction might explore Viserys' relationship with his sister Daenerys in a more in - depth way. For example, it could show how they might have worked together more effectively if Viserys had been less cruel and more strategic. In this fanfiction, Viserys could have been a mentor to Daenerys, teaching her about the history and politics of Westeros.
Another plot might be Viserys traveling back in time. He gets a chance to relive certain events. This time, he decides to be more diplomatic. For instance, he tries to form an alliance with the Starks early on. This could lead to a completely different chain of events in the 'Game of Thrones' universe, with the North and the Targaryens working together against common enemies.
Another theme is family. Just like in the original lore, the relationships with family members play a big role. In these fanfics, a female Viserys might have different dynamics with her siblings, parents or children. Maybe she has to fight against the traditional family roles that are imposed on her. For instance, she could be in a situation where she has to prove herself worthy to her father who doubts a female's ability to rule.
One interesting Viserys fanfiction could be one that explores his early days before the events of the show. It might show his relationship with his family in more depth. For example, how he interacted with his siblings and what his dreams were for the future of his house. Another could be a fanfiction where Viserys survives and has to face the consequences of his actions in a different way, perhaps learning from his mistakes and trying to redeem himself. A third could be a fanfiction that delves into a romantic relationship for Viserys that was never explored in the original series, giving a new dimension to his character.