$b\to s{\mathrm{\ell }}^{+}{\mathrm{\ell }}^{-}(\mathrm{\ell }=e,\mu ,\tau )$ and $b\to s\nu \bar{\nu }$ at Belle and Belle II

The Belle and Belle~II experiments have accumulated a combined data set of $1.2{\mathrm{a}\mathrm{b}}^{-1}$ of $e^{+}{e}^{-}\to B\bar{B}$ collisions at the $\mathrm{{\rm Y}}(4S)$ resonance. Owing to the clean event environment and the well-constrained initial-state kinematics, these data are particularly well suited for studying channels involving missing energy from neutrinos. This includes the reinterpretation of $B^{+}\to K^{+}\nu \bar{\nu }$ and the first inclusive measurement of $B\to X_s\nu \bar{\nu }$ with the missing energy directly from $B$ decays, as well as searches involving missing energy from $\tau$ decays, such as $B^0\to K^{\ast 0}{\tau }^{+}{\tau }^{-}$, $B^0\to K_S^0{\tau }^{+}{\tau }^{-}$, and $B^{+}\to K^{+}{\tau }^{+}{\tau }^{-}$.