Older Brothers Can Marry Their Younger Brothers’ Girlfriends
While it might be hard to believe and likely hasn’t been enforced in a long time, it’s still on the books. So, if you have an older brother, it’s advisable to keep him away from your girlfriend. According to Japanese law and custom, if an older brother expresses a desire for his younger sibling’s partner and pledges to uphold her and the family’s honor, then neither the brother nor the girlfriend can legally refuse.
Indeed, Japan in the previous centuries seems to have been quite an intriguing and dynamic locale.