A joint oscillation analysis of atmospheric neutrinos at Super-Kamiokande (SK) and accelerator neutrinos at Tokai-to-Kamioka (T2K) is in preparation. Apart from the increase in statistics and the lifting of degeneracies providing improved constraints on oscillation parameters, the systematics in T2K and SK’s analyses share many common features and have been carefully studied for the joint analysis. SK is also T2K’s far detector, and a natural correlation between detector systematics exists. Two approaches have been developed; one studying the official inputs to each analysis and evaluating their correlations, and the other simultaneously fitting the underlying observables in the oscillation analysis. A sizeable fraction of SK’s “sub-GeV” events share phase space with T2K’s narrow-band beam. A joint neutrino interaction model has been developed, which allows reducing uncertainties on SK’s “sub-GeV” selections further by using high-statistics data collected at T2K’s near detector, ND280. Additional systematics are introduced to account for phase space not covered by ND280. This poster presents on these new developments and their utility in the joint analysis.