Naming and registering and problems

My japanese partner and I are having a child in Australia in 5 weeks time. We are not married. Our intention is to register the baby with a middle name and my surname in aus on the birth certificate and passport. We then intend to register with japanese consulate using my partners surname, thinking that mine would appear in brackets as would the middle name. Am I totally wrong? And will us not being currently married cause unsolvable long term problems? Too late to do anything about it now but we are now both stressing over the doubt. Thanks

Your name is gDanielh so I am assuming you are the Australian father-to-be, and the mother-to-be is Japanese.

When the baby is born, you get a local birth certificate (with the names the two of you have chosen), and she can take it to the Japanese consulate to register the birth with the Japanese authorities. Since you are not in her gkosekih (Japanese family registry), the child will be entered into her gkosekih as her child, with the name as it appears on the birth certificate. (I am not sure about your surname.)

Have your Japanese partner read the following blog entry about middle name.
Since there is no concept of gmiddle nameh in Japan, the two given names will be strung up together. But there is a way to put a note on it to avoid that, and the process is described in the following blog:
https://ifura.net/middle-names-for-japanese/

The form for registering the birth is among different forms here:
https://www.mofa.go.jp/mofaj/toko/todoke/koseki/index.html

When a Japanese gives birth in Japan, one needs to report it within 14 days, and when outside Japan, I believe it is within 3 months.

Since the mom-to-be is Japanese, by birth the child will be eligible for Japanese citizenship. Please check with the Japanese consulate if there is any additional procedure needed to ensure the baby gets both citizenships.

About potential issues over long-term: if you decide to move to Japan, your child will be Japanese but you are not, so youfd need a visa to enter/stay in Japan, and if you are not married you would not be eligible for gSpouse of Japaneseh visa. I donft know how that is in Australia. Best wishes.