Half Japanese Half Filipina

Hello, hope I can get answers here. I have a japanese passport but not yet tried going to Japan, I am here in the Philippines. My father is japanese and he stayed here for good, I would like to know if It’s okay not to get a certificate of recognition for a Filipino Citizen, can I just get a Philippine passport instead? When going to Japan? Also, is there another option to request Koseki online without a postal check and ems envelope? I don't have anyone to buy in Japan, I have 2 kids and would like to get their Japanese passports as well, I registered them to Japan embassy when they were born. Thanks!

If you travel on a Philapines passport. You need to apply for a visa and can stay a maximum of 15 days.

Travel on a your Japanese passport. There would be zero entry conditions.

Which city are your children's koseki located at? Each city has a different policy on how one could obtain a koseki copy.

Hello gunma ken kiryu

Below are the details on how one can obtain koseki from Kiryu, but it doesn't say what you can do in your case. Why not send them an inquiry? Click お問い合わせは専用フォームをご利用ください。and fill in the form. I also wonder if you've asked your local Japanese Embassy for assistance.

https://www.city.kiryu.lg.jp/kurashi/juminhyo/koseki/1000652.html

Thank you