Of the 120 million people here the number of Protestant Christians is less than 0.5% and is not growing. So in one sense the whole population is unreached. However particularly unreached segments are
The education system puts tremendous demands on these children. Besides massive amounts of homework, in order to enter a good university the serious student is expected to go to cram school after hours. One high school girl who comes to our English class had to attend cram school every day of her recent summer holidays. Many burnout before reaching university. Few come to church.
These are the workers for the big corporations. Much is made of their contribution to the prosperity of modern Japan, but one isnt told how their families suffer. They are expected to devote themselves to their company no matter what. Every 3 years they are transferred to a different city in Japan. Their families often opt to stay put for the sake of the childrens schooling so that the husband goes by himself. Those who have faith are likely to lose it as any resistance to the status quo such as not bowing at the company shrine or asking to have Sundays off will ruin ones promotion chances and lead to life becoming intolerable.
Those born before the war are steeped in Japanese Buddhism/Shinto. They cant understand the new generation let alone a foreigner trying to speak Japanese. Many live a cloistered existence hardly meeting anybody or coming to the door. They are certainly not searching for something to revolutionize their lives. Change is dreaded. Those in old age homes especially live regimented lives and have little or no contact with society.
As you can guess most congregations are made up of housewives, primary school children, students and a few men who are either self employed or work for small companies.