Board Thread:Manga/@comment-39898841-20190622181312/@comment-33077628-20200614195445

TinyHargreaves wrote: I completely understand your confusion; what you're saying didn't make sense to me either which is why I chose to believe Ymir just had control over all the regular human Eldians. But if that's unlikely, it's quite possible she literally will only follow the commands of her descendants based on their surname, like you said... very murky. Abdou250 wrote: It was stated that the first king of the walls did left some of his family outside the walls,however, they are all dead now,probably in the insurection when Kruger's father and his allies were burned alive,and Dina, Eren and some Eldians survived the uprising,after that, Zeke is the only survivor left from royal family outside the walls, and because he never said that to anyone,it was believed by Marley that the royal family inside the walls are the only ones left. Yeah, it's a bit convenient for the author to solve this problem with one line, "they are all dead", but considering how convoluted this is, to me it's good enough.

But I'm satisfied now with the hypothesis that the "Royal Bloodline" is determined by your original family name, kinda like Jon Snow, born Aegon Targaryen. What matters is the "birth certificate", or for Ymir, she looks back into your memories and sees what your mother called you when you were born.

The only problem now are the other descendents from Karl Fritz inside the walls, Uri's Reiss uncles, etc. I can imagine that, since they knew being part of the royal bloodline meant you could one day have to become a titan, eat your relative, inherit his memories, be bound by the will of the "First" King, and only live for another 13 years. So, it's not unreasonable to think many of the siblings would choose to adopt a different name, from their spouse, and live their own lives separate from this "royal curse". This could explain why there are no other "official" royal descendents inside the walls.