@ Vigo_to_Vigo
in my post I was pointing out to seeker that while calling them foster sibling might be more technically correct, based on what has been revealed thus far, it comes across with the wrong impressions, and as far as adoption goes, I haven't seen any proof they DID legally adopt him...sure they took him in when he was little, but he's not living with them anymore, it isn't stated if they are supporting him or not (but given his job using his powers for the gov, I'm guessing not), and anything else beyond that hasn't been stated yet
now I'll admit I'm not familiar with Japanese adoption laws or customs, but the "my parents died when I was young so their friends took me in but now I'm living on my own via jobs/inheritance and their kid who happens to be of the opposite gender, happens to be about the same age, is good looking, and kinda seems to like me keeps poking in on me uninvited" thing is a cliche used in way too many series, and, as such, tends to be my default assumption with a situation like this unless proven otherwise