Not only does Japan have a Demographic slide underway, it has a actual retreat from the procreation imperative that drives individuals to overcome social constraints.
This situation has come about because of flawed National policy even if that is not particularly clear what the flaws are. We can truly blame the government for this situation. So we must start with the stick of a serious loss in pension benefits. Those released benefits can then be applied to assist those that do produce children. Other rewards also are likely needed as well such as a guaranteed minimum wage for stay at home mothers who take on child care for those working.