Board Thread:Theories/@comment-24894791-20160325014734/@comment-25943584-20170820164217

They both are the only Japanese characters in the show. And in the episode where the 3 men tried to kidnap Mikasa they said that she has recesive genes and would be sold to prostitution and the other guy argued that she's too young and that he "wouldn't go at it". And in the manga it says that Levi's mother was also a prostitute and died when he was young so there's a strong possibility they are related.