For a quick island getaway from Tokyo, Niijima in the Izu Islands is a great choice.
Approximately 3 hours by high-speed jet ferry from Takeshiba Pier near Hamamatsucho Station, Niijima is home to stunning beaches (comparable to those in Hawaii or Okinawa), while remaining a hidden gem with not as many tourists. I only discovered this tropical paradise thanks to a friend who runs a minshuku (traditional Japanese bed and breakfast) there.
I was captivated by the island as soon as I arrived, and I am sure you will be too!
Niijima: https://tokyoislands.jp/niijima
Google Maps: https://maps.app.goo.gl/kvxr79T6w7pXcq3f6