Rare decays of the 𝐵-meson that proceed via the underlying quark-level transition 𝑏 → 𝑠ℓ +ℓ − are sensitive probes of physics beyond the standard model (SM). In recent years, measurements of several observables related to these rare 𝐵-decays have hinted at possible deviations from SM predictions. Examples include the Lepton Flavor Universality ratios 𝑅(𝐾) and 𝑅(𝐾 ∗ ), which describe how often a 𝐵 meson decays into a 𝐾 (or 𝐾 ∗ ) meson and a pair of muons or electrons, and are theoretically precise. We present the recent measurement of 𝑅(𝐾) and searches conducted for the Lepton Flavor Violation in 𝐵 decays at Belle. We also discuss the plans related to these rare 𝐵 decays with a larger data sample at Belle II.
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