I'm not sure specifically as I haven't read it in detail. But generally, it might be about the ascension or the growing power of a dark lord, perhaps his origin, his evil plans, and the challenges that the protagonists face against him.
In the 'rise of the dark lord novel', the main character is likely to be the dark lord. However, there may also be characters like his minions or followers who play important roles in his rise. On the other side, there could be a wizard or a knight who tries to stop him, and they would also be main characters in the sense that they drive the plot in opposition to the dark lord.
One potential 'Dark Lord' could be Lelouch. Since he already has the power of Geass and is a complex character, it's easy to imagine a scenario where he succumbs to the darker side of his power. His intelligence and strategic mind could be used for more malevolent purposes.
It could be that the 'Rise of the Dark Lord' is a consequence of some event that went differently in the fanfiction compared to the original series. For instance, if Lelouch made different choices regarding the use of his Geass. Maybe he became corrupted by the power and started to rule with an iron fist, thus becoming the 'Dark Lord'. This would change the relationships he had with his friends and allies, like Suzaku. And the story would be about the chaos and destruction that follows as he ascends to this dark position, and the efforts of those who oppose him to bring him down.
The dark lord's rise in the fanfiction might involve his manipulation of political situations within the wizarding world. He could start by influencing key figures in the Ministry of Magic. Then, there could be a series of mysterious disappearances or strange accidents that are actually his doing, all part of his plan to create chaos and rise to power.
One key element could be the transformation of a character into a dark lord. This might involve a change in their values, goals, and the way they use magic. For example, they could start using dark magic more frequently and become more power - hungry. Another element could be the impact on the wizarding world. The rise of a dark lord would likely bring chaos, fear, and a change in the power dynamics. There might also be a group of characters who oppose this rise, like Harry Potter and his friends, and their struggle against the dark forces would be an important part of the fanfiction.
I'm not entirely sure as I haven't read it specifically. But generally, a 'dark rise' novel might be about the emergence of dark forces, perhaps in a fantasy or horror setting where these dark elements start to gain power and disrupt the normal order of things.