A common theme is the battle between good and evil. Twilight represents good with her magic and kind heart, while King Sombra is the embodiment of evil. Another theme is the power struggle. Twilight's magic power is often pitted against King Sombra's dark powers. For example, in many fanfictions, they have magical duels to determine the fate of Equestria.
One of the main themes is redemption. Sometimes, fanfictions explore the idea of King Sombra being redeemed through Twilight's influence. This can involve Twilight showing him kindness or teaching him about friendship. Another theme is the exploration of the unknown. Since King Sombra has a mysterious past, fanfictions often delve into that, with Twilight being the one to uncover the secrets. It can lead to some really interesting plot twists and character development. There are also themes related to loyalty and sacrifice, as Twilight may have to make sacrifices to stop King Sombra's evil plans.
In 'My Little Pony King Sombra and Twilight' fanfiction, a frequently seen theme is the clash of ideologies. Twilight believes in the power of friendship and harmony, while King Sombra is all about domination and darkness. This leads to their interactions being full of tension. Also, the theme of discovery is common. Twilight discovers new aspects of magic or history while dealing with King Sombra. It could be something about an ancient spell that King Sombra used or a hidden part of Equestria's past. Additionally, the theme of growth is present. Both characters may grow in different ways through their encounters, Twilight in her understanding of true evil and King Sombra, if redeemed, in his understanding of good.
One common theme is redemption. Given Sombra's dark nature, many fanfictions explore Twilight's attempts to bring out the good in him. Another theme could be the power struggle. Twilight's magic of friendship against Sombra's dark magic.
Power is a common theme. Sombra is often depicted as a powerful and sometimes power - hungry character, so fanfictions explore how he wields or tries to regain his power. Another theme is redemption. Some fanfics try to give Sombra a chance at redemption, showing his possible change from a villain to a more positive figure. And there's also the theme of mystery as Sombra has a somewhat mysterious past that many fanfictions attempt to uncover.
In 'My Little Pony King Sombra x Fluttershy fanfiction', a prevalent theme is the exploration of good versus evil within the context of their relationship. Fluttershy represents good, and King Sombra represents evil. So, many stories will revolve around whether Fluttershy can influence King Sombra to turn towards the good side. Another theme is the clash of their worlds. King Sombra's dark and shadowy realm compared to Fluttershy's more idyllic and peaceful world. This contrast can lead to interesting plot developments as they interact and try to understand each other.
The theme of forgiveness is also quite common. Luna, being a more benevolent character, might be in a position to forgive Sombra for his past wrongdoings. This can lead to some really emotional and character - building moments in the fanfiction. Also, the theme of magic and its consequences is often explored. How their magic affects themselves and the world around them is a big part of many of these stories. For example, Sombra's dark magic might have unforeseen consequences that Luna has to deal with, or vice versa.
Celestia is often paired with King Sombra. Their power levels are somewhat similar, and they represent opposite sides of good and evil, so it makes for an interesting dynamic. Twilight Sparkle is also a common character to be paired with him. Given Twilight's knowledge of magic, she could either be in a battle of wits with Sombra or trying to understand his magic for some reason.
Their relationship could start off as one of pure enmity. Twilight would see King Sombra as a great threat to Equestria. But as the story progresses, if they were forced to interact more, Twilight might start to see some small glimmers of humanity (or pony - ity) in Sombra. For example, she might notice that he has a love for a certain kind of magic that is not entirely evil.
One idea could be that Twilight discovers a way to redeem King Sombra. She uses her magic and knowledge to break through his dark exterior and find the good within him. Maybe she uncovers a tragic past that led him to become so evil.
One plot idea could be that Twilight has to enter the realm where King Sombra was banished to retrieve a powerful magic artifact. Along the way, she discovers secrets about Sombra's past that make her question if he was truly all evil. Another could be a time - travel plot where Twilight goes back in time and has to prevent King Sombra from ever rising to power in the first place. Maybe she teams up with an ancestor of one of her friends.
The relationship could start with hostility. King Sombra being the dark entity he is, would see Twilight as a threat. But as Twilight tries to understand his motives, she could start to chip away at his cold exterior. For example, by showing him acts of kindness and mercy that he may not have experienced before.
One popular 'My Little Pony King Sombra and Twilight' fanfiction is 'The Battle Against Darkness'. It shows an intense encounter between Twilight and King Sombra where Twilight uses her magic to try and stop Sombra's evil plans. Another one could be 'Twilight's Encounter with King Sombra's Legacy' which delves into how Twilight deals with the remnants of Sombra's power even after his defeat.