Board Thread:Wiki/@comment-30049797-20160924003216/@comment-29958651-20160924201219

Manuel de la Fuente is absolutelly right. I mean, we actually don't even know how the adoption works in the world of the AoT. As for the relationship between Eren and Mikasa, they could be viewed as a siblings, since they both were raised under Grisha and Carla, but as for the legal point of view, they still could be viewed as a members of two different families (even if the one actually don't exist anymore). The whole issue about adoptions used to be a big mess even in our world (ancient Egypt, antic Greece, the Middle Ages), not to mention the world of AoT. I personally don't think that the Royal Government cared about these type of problems, although the amount of orphans in the AoT world have to be really high.

The surname argument is not as that important. I agree that it is very common to change the surname (in ancient Rome even the whole name) for adopted children, but I think that (if they want), in some countries, they could also keep their original one (Mikasa was actually old enough to remember the life with her true parents, so maybe that's the reason why she kept the original surname).