Another theme is the struggle between the light and dark side of the Force. Since Anakin eventually turned to the dark side, fanfics like to play with this idea. They might show Obi - Wan trying to bring Anakin back to the light, or Anakin trying to convince Obi - Wan that the dark side has its merits in certain situations.
In many Obi - Wan and Anakin fanfictions, the theme of mentorship is key. Obi - Wan's role as Anakin's teacher and guide is central. Also, the idea of destiny plays a part. Whether they can fulfill their destinies together or separately is a common plot point. Additionally, the theme of sacrifice is present, as both characters are in a position where they may have to sacrifice for the greater good or for each other.
The struggle between the light and dark side is also common. Since we know Anakin's fate, fanfictions often play with the idea of Obi - Wan trying to keep Anakin on the path of the light. It's about the internal and external battles they face in relation to the Force.
There's the theme of trust. In a lot of Anakin and Obi - Wan fanfic, their trust in each other is either strengthened or tested. Another theme is the idea of destiny. How Anakin's destiny as the Chosen One and Obi - Wan's role in it are explored. And the theme of sacrifice. Fanfics might show how they are willing to sacrifice for each other, which is a big part of their relationship.
In many fanfictions, Obi - Wan might use his deep knowledge of the Force. He could reach out to Anakin through a Force - bond, calming his inner turmoil and guiding him away from the dark side. For example, he might remind Anakin of their past together, their training, and the values they once held dear.
Maybe the Force itself could be an antagonist in a sense. The light side of the Force would be trying to pull Obi - Wan back from the dark side. And the natural balance of the Force that doesn't want too much dark side influence could be working against Anakin's plan to turn Obi - Wan. So the Force, in its own way, could be the main antagonist.
One common theme is loyalty. Their love is often intertwined with their loyalty to each other as Jedi. For example, in many fanfictions, they will put each other's safety above their own due to their love. Another theme is sacrifice. They might be willing to sacrifice their own standing in the Jedi Order for the sake of their relationship.
Another theme is loyalty. They are master and apprentice, and their loyalty to each other is often tested. In some fanfics, they face situations where they have to choose between their loyalty to the Jedi Order and to each other. This can lead to some really intense storylines.
One common theme is betrayal. Anakin's actions, often related to his turn to the dark side, are seen as a betrayal of Obi - Wan's trust. This creates a deep sense of hurt in Obi - Wan.