Hahajima is the quieter inhabited island, reached by a separate ferry from Chichijima. It has fewer services and far fewer visitors, which is exactly its appeal: forest tracks, small beaches, and a slower rhythm than the already-remote main island.
The island is especially good for walkers and birders. If your Ogasawara trip is long enough, Hahajima turns the journey from a Chichijima stay into a fuller sense of the archipelago.