Electronic correlations have become a central subject of condensed matter physics as a source of the Mott insulator, magnetism, superconductivity, and so on. Over the last decade, they have been known to become remarkably strong in multiorbital systems as the Hund’s coupling plays a significant role. The Hund’s-coupling-driven correlations differing from ones in the proximity of Mottness yield large contributions of local moments at low temperature, their scatterings with incoherent electronic transport, and strong orbital selectivity. We show that the effects of the Hund’s coupling are strongly dependent on electronic structures within density functional theory and dynamical mean-field theory with an exact diagonalization solver. Our systematic approach to ruthenate-based materials and realistic models can reveal that the van Hove singularity modulates the Hund’s metallicity in good agreement with experimental observations. Our theoretical and experimental studies also verify that the monolayer-film ruthenate systems provide a suitable playground for testing the Hundness, the Mottness, and their interplay with electronic structures