Description
The Belle and Belle II experiments have collected a 1.2 ab$^{-1}$ sample of $e^+ e^-\to B\bar{B}$ collisions at a centre-of-mass energy corresponding to the $\Upsilon(4S)$ resonance. These data, with low particle multiplicity and constrained initial state kinematics, are an ideal environment to search for rare electroweak penguin $B$ decays and lepton-flavour-violating $B$ decays to final states with missing energy from neutrinos.
Results from $b\to s\nu\bar{\nu}$ processes and their interpretation are presented. In addition, we present searches for the processes $B\to K^{(*)}\tau^+\tau^-$. Finally, we present our search for the lepton-flavour violating decay $B^0\to K^{*0}\tau^{\pm}\ell^{\mp}$, where $\ell$ is an electron or muon, is described.
