One common theme is loyalty. They are both important figures in the monster world, and stories often explore how loyal they are to each other and to their respective causes.
There are also fanfictions that focus on a more emotional aspect of their relationship. Maybe Gaster has some secrets that only Asgore can understand, or vice versa. They might support each other through difficult times, like when Asgore is feeling the pressure of leading the monsters.
You can try some popular fanfiction websites like Archive of Our Own (AO3). It has a large collection of Undertale fanfictions, and you might be able to find Gaster x Asgore yaoi ones by using the search function.
There might be a fanfiction where Gaster, with his mysterious past and knowledge, helps Asgore deal with the guilt of past actions. As they spend time together, they discover new sides of each other and a yaoi - themed relationship blossoms. It could involve Gaster showing Asgore different perspectives on leadership and forgiveness.
One common theme could be the exploration of their relationship in the context of the outertale universe. It might involve how they interact with the unique settings and other characters in that AU.
There could be some. You might want to check out fanfiction websites like Archive of Our Own. However, the availability and quality can vary. Sometimes it takes some searching through different tags and filters to find the really good ones.
Sure. A lot of fanfics in this pairing play with the idea of what could have been different in the game's story. For example, some might show how sans and asgore could have worked together more closely to change the fate of the Underground. They might also explore the emotional bonds between them, like a deep sense of loyalty or a shared hope for a better future for their kind.
One common theme is redemption. Given their past actions and the rift between them, many fanfictions explore how they can redeem themselves in each other's eyes. Another theme is forgiveness. They have to forgive each other for things like the war and the separation. For example, in some fanfics, they slowly come to understand each other's motives and forgive.
Another theme is redemption. Asgore might have made some mistakes in the original story, and in these fanfics, Asriel can play a role in his redemption process. It shows how love and family can be a driving force for change. For example, in some fanfics, Asriel helps Asgore come to terms with his past actions and move towards a better future. This often involves a lot of emotional conversations and growth for both characters.