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We report photometric and spectroscopic observations of the eclipsing SUUMa-type dwarf nova ASASSN-18aan. We observed the 2018 superoutburst with 2.3mag brightening and found the orbital period ($P_{\rm orb}$) to be 0.149454(3)d, or 3.59 hr. This is longward of the period gap, establishing ASASSN-18aan asone of a small number of long-$P_{\rm orb}$ SU UMa-type dwarf novae. Theestimated mass ratio, ($q=M_2/M_1 = 0.278(1)$), is almost identical to theupper limit of tidal instability by the 3:1 resonance. From eclipses, we foundthat the accretion disk at the onset of the superoutburst may reach the 3:1resonance radius, suggesting that the superoutburst of ASASSN-18aan resultsfrom the tidal instability. Considering the case of long-$P_{\rm orb}$ WZSge-type dwarf novae, we suggest that the tidal dissipation at the tidaltruncation radius is enough to induce SU UMa-like behavior in relativelyhigh-$q$ systems such as SU UMa-type dwarf novae, but that this is no longereffective in low-$q$ systems such as WZ Sge-type dwarf novae. The unusualnature of the system extends to the secondary star, for which we find aspectral type of G9, much earlier than typical for the orbital period, and asecondary mass $M_2$ of around 0.18 M$_{\odot}$, smaller than expected for theorbital period and the secondary's spectral type. We also see indications ofenhanced sodium abundance in the secondary's spectrum. Anomalously hotsecondaries are seen in a modest number of other CVs and related objects. Thesesystems evidently underwent significant nuclear evolution before the onset ofmass transfer. In the case of ASASSN-18aan, this apparently resulted in a massratio lower than typically found at the system's $P_{\rm orb}$, which mayaccount for the occurrence of a superoutburst at this relatively long period.

ASASSN-18aan: An Eclipsing SU UMa-type Cataclysmic Variable with a 3.6-hour Orbital Period and a Late G-type Secondary Star