Long-term optical to hard-X-ray variability of RT Cru. Panel a: RT Cru optical B- and V-band light curves with measurements from Cieslinski et al. (1994, black plus signs), ASAS (gray dots), AAVSO (black crosses for the V band, red circles for the B band), and ASAS-SN (open circles). Panel b: B − V curve from AAVSO data. Panel c: Swift/UVOT UVM2 (open circles) and UVW2 (blue dots) light curves. Panel d: Swift/BAT 14−50 keV measurements (light blue dots) with 100-day bins (with 1σ error bars). The maximum in the BAT light curve around 2011−2013 is due to an increase in the accretion rate, which did not increase enough to reach the level where the boundary layer becomes optically thick and a super-soft X-ray component arises (see Luna et al. 2018b). Between late 2019 and late 2020, RT Cru was not detected by Swift/BAT in 100-days bins. Panel e: Swift/XRT 0.3−10 keV count rate in log scale to highlight the fade in flux in 2019. Panel f: Swift/XRT softness ratio. Panel g: Hα (blue dots) and adjacent continuum (yellow dots) flux evolution. Panel h: He I 6678 Å (red dots) and adjacent continuum (black dots) flux evolution. Starting around mid-2017, the B − V color became redder for a few years (panel b), during which time the hard X-ray flux dipped (panel d). The UV and soft X-ray emission (panels c and e) also dipped at around that same time.