Responses
Yeah its different in Japan. And The aunt take advantage of it. In Japan if you don't write it on the paper or make it clear who you want to give your will to, most likely it would fall to the second generation or your closest blood relatives (in this case the aunt). As so many guessed, the Grandma probably leave a will for the grandkids, but the aunt hide it so she would have all of the wealth the grandma left.
Anyone I didn't get that part