A message from Anonymous
The name of Eren's father is Grisha, the diminutive of Grigori in Russian. We know that Isayama don't choose his characters' names randomly. In one biblical apocrypha, the "Grigori" are known as fallen angels who mated with women, giving birth to the Nephilims (human-angel hybrids) , who are described as GIANTS in the Genesis. I think (if it's not too far-fetched) that it may be a clue about some mysteries of SnK. Sorry for my bad English.