Another plotline could be a time - travel scenario. Draco gets sent back in time to Camelot. He becomes an apprentice or a follower of Arthur Pendragon. He then has to learn the ways of Arthur's court, deal with the politics and magic there, and in the process, he grows as a person, bringing back some of Arthur's wisdom to his own time when he eventually returns.
One possible reason could be a misunderstanding. Maybe Merlin did something that Arthur misinterpreted as betrayal or dishonesty. For example, if Merlin was secretly helping an enemy for a greater good that Arthur wasn't aware of at the time.
One possible plotline could be Arthur trying to escape the whore house and regain his honor. He might meet some unlikely allies among the people there who help him plan his escape.
Saber from Fate/Stay Night would be an obvious choice. Since she is also related to the Arthurian legend, there could be a lot of interesting interactions between them. They could compare their experiences as king, or even fight side by side against a common enemy.
Well, one way could be through magic. Maybe there's a powerful spell that creates a portal between Draco's magical world (say the wizarding world of Harry Potter) and Arthur Pendragon's Camelot. Through this portal, characters from both worlds can interact, and their cultures and magic systems start to blend. For example, wizards from Draco's world might introduce new spells to Camelot, while Arthur's knights could teach the wizards about chivalry.
In some fanfictions, the heir of Arthur Pendragon could have a special connection to the magical creatures in the Harry Potter universe. Since Arthur was a great king, the heir might inherit his ability to communicate or form bonds with these creatures. This connection could be crucial in solving various mysteries in the wizarding world, like finding a hidden place where a powerful dark magic object is hidden. They could use the help of these creatures to outwit the villains who are also after the same object.
One possible plotline could be that Harry discovers he has a secret heritage as Lord Pendragon. This leads to him having new powers and responsibilities. He might have to face off against enemies from both the wizarding world and the Pendragon - related threats.
One possible plotline could be that Harry, through some magical accident or inheritance, comes to own Draco's family manor. Draco is then forced to interact with Harry on Harry's terms to regain his family's pride. Another could be that Harry wins a bet against Draco and the terms of the bet are such that Harry now has ownership over Draco's time, making Draco do tasks for Harry.
Another plot could be Draco dealing with his family's fall from grace. His family had strong ties to the Dark side during the war, and now he has to figure out how to navigate a world where his family name doesn't hold the same power. He could be struggling to find his own identity outside of his family's reputation.
A plotline could involve Draco's family trying to hide his non - pure - blood origin for generations. When Draco finds out, he could start to question his family's values and actions. He might then try to find out who his non - pure - blood ancestors were and what their story was. Maybe he forms an unlikely alliance with some non - pure - blood characters in Hogwarts as he tries to come to terms with his new identity. There could also be a plot where the discovery of his non - pure - blood status changes his relationship with Harry Potter. Instead of being rivals, they could become allies as Draco realizes the unfairness of the blood - based discrimination in the wizarding world.
Maybe Draco discovers a powerful magical artifact that can defeat Voldemort and he decides to use it for the greater good, even if it means going against his family's past allegiances. He could then face many challenges and battles before finally being able to kill Voldemort.