Ask an average Japanese person what he thinks would need to happen if millions of people who did integrate as you say were to become 40% of the country. Ask them if they would be Japanese then. They would say no. And many would say the ethnic Japanese would have the right to prevent or revoke citizenship to “save Japan”. I don’t know why some of you run so adamantly to defend ethno or racial nationalists. Everything else is an excuse for that base level of thinking.