Top panel: HSC colour image (band: grz) of the windy QSO XID439. The cutout size is ~25′′ on side. The dashed rectangle highlights the area in which the host galaxy-AGN decomposition was performed. Bottom panel: host galaxy-AGN decomposition on Subaru i-band data. The panels from left to right are a zoom in the central area of the top panel (dashed rectangle, ~10′′ in size) as follows: (1) observed HSC i-band image, (2) best-fit point source + galaxy model, (3) data minus the point source model (i.e., the pure-galaxy image), (4) data minus the galaxy model (i.e. the pure-AGN image); and (5) fitting residual divided by the variance map. In all panels, north is up and east is left.