Host galaxies associated with the ultra-strong Mg II absorbers. The postage stamp HSC color composite images centered on the quasar are depicted with gray contours. The SDSS fiber, with a radius of 1.5″, is indicated by dashed circles, while the cyan-colored aperture highlights the USMgII host galaxy. The first three rows exhibit an example set of potential host detections at close quasar proximity for USMgII systems with direct [O II] detection (at the 2σ level) followed by [O II] detections at the < 2σ level in rows 4−7. The bottom two rows display cases with no detection around the quasar. Additionally, the right panels showcase the stacked [O II] emission line profiles, and the gray curve shows the associated error.