Koseki – birth out of wedlock

**Im not pregnant and dont plan to be anytime soon** but I came across something today while reading up on Koseki laws that confused me a little bit.

If im understanding correctly, if a child is born out of wedlock to a foreign national mother (without citizenship), and the father is a Japanese national, he needs to file a 認知届 before the child is born to acknowledge paternity. Reading up on this now I saw it has to be done voluntarily. My question is what happens if the man doesnt acknowledge? Is that kid just stuck without being considered a Japanese citizen and having all the issues that come with not being registered to a Koseki?

Is there no recourse that can be taken by the mother towards a father that refuses to take responsibility in Japan?

If im interpreting this law wrong please correct me! Im genuinely interested in learning and understanding.

by Higgz221