  We present a general relativistic, ray-tracing radiative transfer code RAIKOU
for multi-wavlength studies of spectra and images including the black hole
shadows around Kerr black holes. Important radiative processes in hot plasmas
around black holes, i.e., (cyclo-)synchrotron, bremsstrahlung
emission/absorption and Compton/inverse-Compton scattering, are incorporated.
The Maxwell-J\"uttner and single/broken power-law electron distribution
functions are implemented to calculate the radiative transfer via both of the
thermal and the nonthermal electrons. Two calculation algorithms are
implemented for studies of both the images and broadband spectra. An
observer-to-emitter algorithm, which inversely solve the radiative transfer
equation from the observer screen to emitting plasmas, is suitable for
efficient calculations of the images, e.g., the black hole shadows, and spectra
without the Compton effects. On the other hand, an emitter-to-observer
algorithm, by which photons are transported with a Monte-Carlo method including
the effects of Compton/inverse-Compton scatterings, enables us to compute
multi-wavelength spectra with their energy bands broadly ranging from radio to
very-high-energy gamma-ray. The code is generally applicable to accretion flows
around Kerr black holes with relativistic jets and winds/coronae with various
mass accretion rate (i.e., radiatively inefficient accretion flows,
super-Eddington accretion flows, and others). We demonstrate an application of
the code to a radiatively innefficent accretion flow onto a supermassive black
hole.
