The universe formed by Kerr black holes

Through a coordinate transformation, we can regard the internal spacetime of a Kerr black hole as a universe. We can utilize a new coordinate system to study the internal spacetime of the Kerr black hole, primarily focusing on the region between the inner event horizon and the outer event horizon. What is the difference between the Kerr black hole universe and the Schwarzschild black hole universe? I am very curious to see what the internal spacetime of a Kerr black hole looks like in the new coordinate system. I didn't expect that just the addition of the rotation condition would make the internal spacetime of a Kerr black hole vastly different from that of a Schwarzschild black hole. This article will discuss how the universe represented by the internal spacetime of a Kerr black hole evolves.