Adoption in Japan
The last time I posted here, the advice I got was super helpful, so I'm back.
I've been researching adoption in Japan, as I've been writing a separated at birth fic. Yes, it's a common trope, but so far I haven't seen many stories in my fandom that set it up in a realistic -- or at least a decently researched -- way, so I've decided to do what I can to change that. The specific fandom doesn't matter -- it only matters that the setting is modern-day Japan.
I've already looked up "Japan family law" and "adoption of minors in Japan," and I've gotten a sense of the attitudes towards adoptions, as well as some the legal issues. For instance, I know adoption is not looked upon too kindly, that the system is fragmented and certain agencies are not reputable, and that kids often stay in institutions for a very long time. The last is true because the official position is that if the biological parents are alive, every effort should be made for kids to eventually return to them (even if it's at the age of 18). I also know there are "regular" and "special" adoptions; in the former, the ties between child and biological parent are not legally severed. In some "special" adoptions, the couple looking to adopt pays the medical expenses of the woman who's about to give birth and give her child up.
The scenario is as follows. The setting is Japan, 2013. There's a brother and a sister -- twins. They're given up for adoption as babies, and are taken by different families because the less-than-reputable agency that orchestrates the Juno-style adoption wants to make some extra money and charge two families for the same medical (and other) bills. Let's say it's also a "special" adoption, and the birth parents are out of the picture once the ink is dry.
The sister's adoptive parents then die in a car crash when she is 15, and shortly after she finds out she has a brother and meets the family that had adopted him back in the day. They all take to each other, and the brother's family offers to take her in and make their guardianship of her official. Now, I've also read up on adult adoption, a common practice in Japan for the purposes of inheritance, and I know that 15 is old enough to be adopted as an "adult" (thanks, Wikipedia). My questions are, though:
1) Is the state likely to intervene at all in this context? After all, the age of majority in Japan is 20, and kids remain in orphanages until age 18.
2) Let's say the girl's adoptive parents' extended family comes out for the funeral. Would she need their permission to be adopted by another family as an "adult"? Would they have legal grounds to contest her decision?
3) If the answer to either of the above questions is "yes," how weighty of an argument would it be that she should be with her brother? I know blood ties are considered quite important in Japan. In this scenario the brother is her only known biological relative, though it might not matter because he's a minor as well.
Basically, I am tempted to orchestrate some sort of legal battle that happens in the background as brother and sister bond, and my questions are geared at figuring out how I should frame it, or whether I should even go there. Any advice would be appreciated.