A very popular theme is the 'alternate universe' or AU. In these fanfics, the Good Omens world is reimagined. For instance, they could be in a modern high school setting, where Aziraphale is the nerdy but kind student and Crowley is the cool rebel. Or they could be in a historical setting, like the Victorian era. These AUs allow for a whole new set of adventures and relationship dynamics for Aziraphale and Crowley.
The idea of them protecting each other is also common. For example, Crowley saving Aziraphale from some angelic danger or vice versa. And then there's the theme of self - discovery. They both have been part of their own 'worlds' for so long, and in fanfics, they often discover new things about themselves through their relationship with the other. It's really interesting to see how different authors play with these themes.
Chapter 688, "Iron Sand Palm Skill Acquired!", is the clearest early answer because the violence around Ji Yanbai becomes final instead of hypothetical. The chapter gives readers a real answer by opening on Shao Changqing was very pleased with Bai Lu.
Chapter 900, "Let You Hold Your Great-Grandchild Sooner!", is the clearest early answer because it turns Jiang Zhao Yuan's situation into a concrete plot event. The chapter gives readers a real answer by opening on The nerve-wracking two days quickly passed.
A practical answer is Chapter 25, because it turns the idea into a concrete scene. The chapter opens with Therefore, from his childhood, Jiang Shixu had felt an extreme aversion to..., adds pressure through When she saw the woman behind the desk, she smiled and said, "Look who..., and ends on.
Chapter 847, "How Else Can You Argue?!", is the clearest early answer because it turns Rong Junsheng's situation into a concrete plot event. It opens with The Rong family couple watched the situation unfold, exchanged a...
Chapter 805, "I Just Want to Eat a Big Chicken Leg!", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event. The chapter gives readers a real answer by opening on The next day, the twins were much quieter.
Chapter 16 is the strongest chapter-level answer because it starts from Just as the words fell, Jiang Shixu swiftly cast his eyes downward. and follows through on Jiang Shixu panicked, set down the bowl, and reached forward to grab her....
If you want the clearest chapter reference, go to Chapter 15. Early on, Jiang Shixu woke up from those nightmares filled with blood and darkness,...; later, the chapter leans on The two sleeping pills he took in the evening had left him with a....
Chapter 857, "Interested in joining us?", is the clearest early answer because it turns Qixing Tower's situation into a concrete plot event.
Chapter 838, "Just Call Me Grandpa", is the clearest early answer because it turns Shi Lei's situation into a concrete plot event. Early on, Gu Qiang's expression was subtle as well.. By the end, It's so difficult to finally meet you." Jiang Li stood up,....
A practical answer is Chapter 23, because it turns the idea into a concrete scene. The chapter opens with Although Jiang Li exerted very little strength, Jiang Yan instantly felt..., adds pressure through So the moment the news broke that Jiang Li was entangling with Shang..., and ends on However.