I'm not entirely sure specifically as it could vary greatly. It might be a fan - created story involving characters named rk800 and rk900. It could be in the context of a science - fiction or tech - related universe.
You could try looking on popular fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. They usually have a large collection of fan - created stories across various genres and fandoms.
Another way they interact is through conflict. RK900 might be programmed with a different set of priorities than RK800. This could lead to clashes between them as they try to achieve their respective goals. However, through these conflicts, they might also come to understand each other better and find common ground in the end.