Well, it could start with Gavin showing a bit of kindness when RK900 is hurt. Maybe he offers some small gesture like getting him a power source when RK900's energy is low. This simple act could be the start of a chain reaction where RK900 starts to trust Gavin more, and they gradually become friends or even closer allies over time.
Their relationship could develop through shared experiences. For example, working on a difficult case together. This would force them to rely on each other and understand each other's strengths. Gavin might see RK900's efficiency and RK900 would see Gavin's intuition.
A possible plot could involve RK900 being hacked and made to perform actions that are against his programming. Gavin discovers this and has to work against time to save RK900 from both the hackers and the potential destruction of his own self - identity. During this process, they form a deep connection that changes their relationship from one of distrust to mutual respect and care.
Sure, in some of the fanfictions, the RK900 and Gavin Lemon pairing offers a lot of room for creativity. Writers can explore their emotions, their conflicts, and their potential for cooperation. It could be a story about them learning to trust each other in a hostile environment, or perhaps a more light - hearted take on their daily interactions.
One common theme is redemption. RK900 is often portrayed as trying to make up for past actions or mistakes that led to his hurt. Another theme is isolation, as he may be shunned or left alone because of his damaged state.