In this fanfiction, it might be that Anakin has a vision of the future where the younglings grow up to be great Jedi and save the galaxy. So, he defies Palpatine's orders. He could enlist the help of some loyal clones or other Jedi who have managed to escape the initial purge. He then takes the younglings to a remote planet where they can be safe and trained in secret.
One common storyline could be Anakin's struggle with his darker side while interacting with the younglings. For example, in some fanfics, Anakin might be forced to protect the younglings from an external threat, which tests his loyalty to the Jedi Order. Another storyline could involve Anakin teaching the younglings, which shows his relationship with the next generation of Jedi. There are also fanfics where the younglings sense Anakin's internal conflict and try to help him, adding an interesting dynamic to the story.
It could be Palpatine. Since Anakin is going against his wishes by saving the younglings, Palpatine would see this as a threat to his plans. He might send more clone troopers or even some of his dark side minions to stop Anakin.
Fanfics often depict Anakin's interaction with younglings as complex. Sometimes he is kind and patient, like a big brother or a mentor. He might teach them lightsaber techniques or how to meditate. But other times, his darker side can peek through. For example, he could get frustrated with their lack of progress, and the readers can see the internal struggle within him as he tries to control his emotions.
As he spends more time as a Sith, he might start to feel a sense of emptiness. He realizes that the power he sought isn't fulfilling. He could then have a moment of self - reflection. Maybe he meets a character who challenges his beliefs, like a young Force - sensitive who still believes in the good in the galaxy. This makes him question his path and start to seek a way back from the dark side.
Well, a very common theme is the internal struggle. Anakin is constantly fighting within himself in these fanfics. There's also the theme of loyalty, whether it's his loyalty to the Sith or any remaining loyalty to his Jedi past. And the theme of revenge often comes up, as he might seek revenge on those he feels wronged him as a Sith.
The novel of Revenge of the Sith is canon. It aligns with the established Star Wars canon framework and adds depth and detail to the events depicted in the movie of the same name.