Dying Former Axis Powers
One striking fact is that three (Germany, Austria and Italy) out of the four countries with the lowest birth rates (Portugal, whose fascist regime was neutral during World War II being the fourth) constituted the principal World War II axis powers. In addition, Japan, the non-European former axis power has birth rates as low as the three European former axis powers.
Is this a coincidence? Probably, at least mostly. It might however also be the case that some people in those countries still feel some collective guilt (which is unjustified because the collective guilt notion is irrational,but which some people might feel anyway) over what happened in the past, and therefore don't feel like creating new people who according to the collective guilt-mentality would share that guilt.