Can i still claim japanese citizenship?

Me and my sister's biological father is japanese while my mother is a filipino citizen. I am now 29 years old. The surname that i use is my fathers surname and his details are stated in my filipino birth certificate. They never got married. When their relationship ended she got married to a japanese national. We were not legally adopted by our stepfather and our details were not registered in japan by our biological father. Currently my parents are residing in japan and we are left here in the Philippines. We would like to migrate and live with our parents but is it still possible for us to acquire japanese citizenship and be able to reside and work there?

There is a lot if "IFs" in your history. I wouldn't said no since your birth was never registered in Japan. But if you have family already their, you might be able to chase that up. But at age 29, I doubt you'll fit into any type of family visa as you are not a dependent child.

Since you have family in Japan, it is probably best that they seek legal advice from an immigration lawyer so you get 100% correct information and also poosible new avenues to chase for visa applications.

My mother was not fully aware of requirements and laws during the 80's. i wouldn't blame her because of her lack of educational background. that is why she left for japan during that time to help her family. i hope we get some idea and info regarding this if there are other people who have similar situations. i will be going back to japan to visit on march and will inquire in the embassy.

If you are not already registered in the family register, it's too late to get citizenship. If you can find your biological father's family register, and prove that you're his son, then it's possible to get a Child of a Japanese visa. There is no age limit for that.

i will be going back to japan to visit on march and will inquire in the embassy.

I hope you mean the Japanese embassy in the Philippines, not the Philippines embassy in Japan.

yes i will be going to the japanese embassy in japan this march. we are currently trying to reach out to my biological father but i believe he is already deceased. all i have is the information regarding the company he owns in japan which is run by my half brother.

japanese embassy in japan
By definition there is No Japanese embassy in Japan. You probably mean that you will go to some ministry in Japan.
I�fd assume you already searched online, but there are several organizations looking into the specific problems of kids with Filipino mothers and Japanese fathers. If you haven�ft yet, it might help to reach out to them.

sorry honest mistake on the terms. we have been asking a lot of people already but it seems there is no clear information regarding my case. hopefully we get some answers when we go to the ministry

could you please give me a sample of the organizations you are referring to?

Well, for example this one: http://www.jfcnet.org/news/other/542/

But I would guess that if you do search in Tagalog or Japanese you should be able to find many more. I am really no expert on this topic at all. Just a very superficial google search.