Cupy is a library for vectorized operations on GPU. It's very similar to NumPy;
cupy.ndarray implementsarray, but it doesn't work since np.asarray(cupy_array) raises an exception. This was done intentionally by the creators to avoid hidden performance issues.
However to convert a cupy array in a numpy array there is the function cupy.asnumpy(...).
As a result, matplotlib cannot natively plot data in cupy arrays: they must converted to numpy before.
Maybe, given that cupy is fairly spread, should be written a workaround so that matplotlib can optionally make the conversion itself.