Well, there isn't really a proper 'love story' between Princess Luna and King Sombra. King Sombra is a dark and power - hungry character. Princess Luna, on the other hand, is associated with the moon and the well - being of Equestria. Their interactions are mostly about Sombra's malevolent plans and Luna's duty to protect her realm. So, it's not a love - based narrative at all.
One possible story could be that Princess Luna, with her connection to the night, tries to understand the darkness within King Sombra. Maybe she believes there is some good left in him despite his evil deeds. She could use her lunar magic to reach into the shadows that surround him and try to communicate with his true self.
Their relationship could develop in a more complex way. Maybe Sombra has a hidden past that Luna discovers, which makes her pity him. This could lead to her trying to help him reform. Sombra, on the other hand, might be initially distrustful but then gradually open up to Luna as she shows him kindness. They could end up as friends or at least allies who have a deep understanding of each other.
Well, one possible plot could be that they start as enemies as in the original lore. But then, an external threat forces them to work together. They gradually learn about each other's pasts and find some common ground. Maybe they both had difficult upbringings in different ways. And in the end, they form an unlikely alliance that changes the power dynamics in Equestria.
Perhaps in the fan fiction, King Sombra has a secret past that is linked to Princess Luna. He was once a pony like any other, but a dark magic experiment gone wrong turned him into the monster he is now. Luna discovers this truth and feels a sense of responsibility for him. She tries to reverse the magic that corrupted him. This involves going on a journey to find the origin of the dark magic, facing many dangerous creatures and challenges along the way. And all the while, Sombra is fighting his own inner demons, not sure if he wants to be saved or if he should continue his path of destruction.
In terms of the plot, it could start with Sombra's return or some sort of threat that he poses. Luna then steps in to deal with it. The setting within the My Little Pony world would be important. It could be set in Canterlot or some other location. The fanfic might also introduce new characters or use existing ones to support the main plotline between Luna and Sombra.
King Sombra was a character full of mystery when it comes to love. He was more interested in ruling and spreading his shadowy influence. But who knows? Maybe there was a love story that was yet to be told. It could be that he had a forbidden love that he had to sacrifice for his ambitions. Or perhaps he was simply too cold - hearted to experience love in the way we understand it. The lack of clear details in the lore makes it an open - ended mystery about his love life.
Their relationship could develop through shared goals. For example, if there is a magical imbalance in Equestria that only their combined magic can fix. As they work towards this goal, they start to understand each other better.
One common theme could be the battle between light and dark. Luna represents the moon and has an association with the night, which can be seen as a time of mystery and sometimes danger. King Sombra is a dark character. So the fanfic may explore this contrast in terms of their powers and personalities.