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.
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.
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.
There are many fanfic communities where 'asgore x asriel fanfic' might be found. For example, FanFiction.net could be a place to start. However, the availability might depend on how active the fandom is in that particular site. Some fanfics might explore their relationship in different ways, like a father - son bonding type of story or something more creative and unique.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). It has a vast collection of fan - made stories, and you're likely to find a good number of 'Asgore x Toriel' ones there. Just use the search function on the site and type in the relevant tags.
One popular 'Asgore x Toriel fanfiction' might be those that explore their past relationship and how they could potentially reconcile. For example, some stories might focus on the emotional journey they go through as they remember the good times before their separation.
Archive of Our Own (AO3) is a great place to start. It has a large collection of fanfics from various fandoms, including Undertale, and you're likely to find some sans x asgore ones there.