Three recent studies on CP violation and related hadronic $B$ meson
decays by the Belle experiment, in particular on determination of the
angle $\phi_1$ of the Unitarity Triangle, are reported. The first joint
analysis by Belle and BaBar focused on time-dependent CP asymmetry of
$B\to D^{(*)}_{CP}h^0$, which is a combination of the tree-only $b\to
c\overline{u}d$ and $b\to u\overline{c}d$ processes, and established CP
asymmetry by $5\sigma$. Using a similar process, $B\to D^{(*)}h^0$ with
$D\to K^0_S\pi^+\pi^-$, a time-dependent Dalitz plot analysis was
performed and excluded the second $\phi_1$ solution by $5\sigma$. A new
$b\to c\overline{c}d$ process, $B\to\psi(2S)\pi^0$, was observed for the
first time. All of these studies are relevant for the ultimate
precision measurement of the Unitarity Triangle angle $\phi_1$ at Belle II.