Latest results on $B\to DK/D\pi$ decays from Belle

The CKM angle $\phi_3$ is less precisely known than the angle $\phi_1$ and the only one that is accessible with tree-level decays in a theoretically clean way. The key method to measure $\phi_3$ is through the interference between $B^+\to D^0 K^+$ and $B^+ \to \bar D^0 K^+$ decays which occurs if the final state of the charm-meson decay is accessible to both the $D^0$ and $\bar D^0$ mesons. To achieve the best sensitivity, a large variety of $D$ and $B$ decay modes is required, which is possible at Belle experiment as almost any final state can be reconstructed including those with photons. The results from Belle, as well as the ongoing studies, are discussed here. The details of the planned measurement at Belle II, a substantial upgrade of the Belle detector which will operate at the SuperKEKB energy-asymmetric $e^+ e^-$ collider, are also discussed. The results from the first collisions at Belle II during April-July 2018 are shown too.