Step daughter's inheritance right

H. Kawarazaki, esq.

Question
My mother is a citizen of Japan, has a green card and resides with me in the US. My mother's sister (Japanese citizen living in Japan) passed away and her step daughter (daughter of her husband's previous marriage) and my mother are the only immediate family left to receive her inheritance.
Another family member insists that all inheritance will go to my mother because she is the only "blood" relative left. My mother is on "not so friendly" terms with the step daughter so she has no one else to speak with in Japan to find out if she is on the Will (if there is one) or have any rights to her sister's inheritance.

Question 1: Does my mother have any rights to the inheritance with or without a will? If so, what percentage?

Question 2: If we can't find out the situation, what official office can we contact here in the States and/or Japan to find out the status of her sister's inheritance?

Answer
Answer 1: If her step daughter was registered as a adopted daughter, her step daughter receives all the inheritance assets. If her step daughter was not registered as a adopted daughter, your mother receives all the inheritance assets.

Answer 2: Your mother can confirm the situation by checking the family registration;"Kosekitohon" in Japan. Your mother can get the copy of the family registration at ward office or city office.

Above 2 answers based on the situation that she left no will.