I love this, because it reminds me that relationships like this do actually exist.
Valuable friendship that transcends boundaries.
That's whats so hard about the friendship/romance line. You don't even have to get too close to the "edge" for things to become fogged and nondescript. Often some of the best romantic relationships get initiated because someone realizes they would want to be with their close friend more than anyone else, and would not want to leave him/her; the romantic feelings follow far quicker than you expect
Can people in Japan not adopt if they're unmarried?
My understanding is the adoption in Japan is actually pretty rare. Abortion isn't as religiously stigmatized there as it is the the US, so unwanted pregnancies probably aren't carried to term as often. I could be wrong about that. Wikipedia said that over 90% of adoptions that happen in Japan are adult adoptions for securing heirs, not infant adoptions.
It's a mix of that, and the fact adopting is far more difficult than you expect. If you try to do it when you are "not a reliable caregiver" (unfortunately, homosexuals get stuck in the same category as psychopaths and repeat fellons), it's like trying to get away with plagiarism on a paper. If you don't have to get away with it, you have nothing to worry about. But if you do try, the check is so thorough and unforgiving that if you let up an inch, they'll burn ya for it.