One idea could be a story that focuses on Anakin's internal struggle between his love for Padme and his fall to the dark side as Darth Vader, while Luke and Leia unknowingly grow up in the shadow of their father's actions. It could explore how their lives might have been different if Anakin had not turned, and how they eventually come to terms with his true identity.
There are quite a few fanfics out there on this topic. You can start by looking on popular fanfic websites like Archive of Our Own. Some might explore the complex relationship between Padme and Vader in this unique scenario, delving into how their story could have been different if Padme was pregnant and they had to face the challenges together, both as a couple and in the context of the Star Wars universe.
One common theme is the struggle between love and the dark side. Darth Vader is on the path of the dark side, but his love for Padme and their unborn child might create an internal conflict. Another theme could be protection, as they would need to protect their family in a dangerous galaxy filled with enemies.
A possible plot is a fanfic where Anakin, in his Darth Vader form, has a vision of a different future where he didn't lose Padme. This vision makes him question his loyalty to the dark side. Meanwhile, Luke and Leia are on a mission to rescue their father from the clutches of the Emperor. The story could be filled with emotional reunions and battles between the light and dark forces.
A possible plot could be that Padme fakes her death as in the original story, but Vader discovers she is alive and pregnant. He then decides to break away from the Empire to start a new life with her and their child, but they must evade the Empire's forces and Vader has to come to terms with his new identity outside of the Sith.
The idea of redemption is a big one. Darth Vader's redemption at the end of Return of the Jedi is a powerful moment, and fanfics often expand on this. They might explore what led to his final choice, or how his family influenced his decision. Additionally, the exploration of the Force and how it connects all these characters is another common theme. It could be about how Luke and Leia develop their Force abilities differently, or how Anakin's relationship with the Force changed over time.
The Sith Order could be one of the main antagonists. They might see Vader's marriage to Padme as a weakness or a deviation from the Sith path. So they could try to undermine their relationship or even harm Padme to bring Vader back to their full control.
At first, it might be full of tension. Vader is now a dark figure, but Padme's pregnancy could be a catalyst for change. He might start to show moments of his old self, Anakin, and they could gradually re - connect on an emotional level.
A possible plotline is their family life. In fanfiction, we might see how they raise their children, if any. Maybe they have to protect their family from the dark forces that Vader is often associated with, while also trying to keep their relationship strong.
One great fanfiction could be 'Love Beyond the Dark Side'. It beautifully explores the complex relationship between Darth Vader and Padme. It delves into their past memories and how their love still lingers despite Vader's fall to the dark side. Another one is 'Padme's Unwavering Love', which focuses on Padme's side of the relationship, showing how she still holds onto her love for Anakin even after he becomes Darth Vader.