Resolving the eightfold neutrino parameter degeneracy by two identical detectors with different baselines

We have shown in a previous paper that two identical detectors with each fiducial mass of 0.27 megaton water, one in Kamioka and the other in Korea, which receive the (anti-) muon neutrino beam of 4 MW power from J-PARC facility have potential of determining the neutrino mass hierarchy and discovering $CP$ violation by resolving the degeneracies associated with them. In this paper, we point out that the same setting has capability of resolving the θ₂₃ octant degeneracy in region where sin²2θ₂₃0.97 at 2 standard deviation confidence level even for very small values of θ₁₃. Altogether, it is demonstrated that one can solve all the eightfold neutrino parameter degeneracies in situ by using the Tokai-to-Kamioka-Korea setting if θ₁₃ is within reach by the next generation superbeam experiments. We also prove the property called ``decoupling between the degeneracies'', which is valid to first-order in perturbation theory of the earth matter effect, that guarantees approximate independence between analyses to solve any one of the three different type of degeneracies.