Much of RAIN is based on 3D environments and characters. The Basic Motor, Basic Navigator, sensors, movement functions, and AI Kinematic all assume a y-up 3D axis. Out of the box, some features are not compatible.
However, many developers have successfully integrated RAIN into 2D games. You can still use the behavior tree system, the Basic Mind, the Memory system, and the overall structure of RAIN. If you do want to integrate movement, sensors, or pathfinding, you can build 2D replacements for the motor, navigator, and sensors and plug them in.