Tau physics and dark sector searches from Belle II

The high luminosity upgrade of the SuperKEKB accelerator offers the Belle II experiment unique oppurtunities to probe the dark sector, lepton universality and lepton flavor violation in the tau-lepton sector. This talk summaries recent world-leading results from the Belle and Belle II experiment on searches in the dark sector. In addition, the world's most precise determination of the tau lepton mass and searches for lepton flavor violation in tau decays into a scalar non-SM particle and a lepton are reported.