There is no public airport in Ogasawara. The standard route is the Ogasawara Maru ferry from Takeshiba Pier in Tokyo to Futami Port on Chichijima. The crossing usually takes about 24 hours, and the ship schedule creates a natural minimum stay of several nights.
Book ferry tickets and lodging well ahead in busy seasons. Weather can delay the sailing, so do not plan a tight international flight connection immediately after returning to Tokyo.