I will give an overview of my ongoing works. First, I introduce Monte Carlo-based 3D
radiative transfer code SKIRT, which was originally set up as a dust radiative transfer
code. Especially, we implement a new module of the non-LTE line radiative transfer
calculations in SKIRT, resulting in a generic and powerful 3D radiative transfer code
that can self-consistently generate spectra with molecular and atomic lines against the
underlying continuum. Now, we are applying the extended SKIRT code on various types of
3D hydrodynamic simulations of an AGN torus and a cosmological galaxy to investigate the
origin of the emission lines and dust continuum.  Second, I discuss the SED evolutions
in isolated galaxy simulations using SKIRT and GADGET4-OSAKA, which incorporate the
evolution of grain size distribution driven by dust production and interstellar
processing.