I just got back from Japan and talked to our guide (who is mainly a birder) about good places to see alot of the endemic mammals. We talked about the rabbit and he said since the Japanese have been working to eradicate the feral mongoose population, it is easier to see them. There are tours that are mainly directed to see the endemic amami thrush at night and he told me every time he has taken people out in the last few years he has seen the rabbit well. Maybe trying to hook up with a local bird tour guide would be the best bet. While the guide is looking at the thrush, your friend can look at the rabbit.