Eren knew about something when she kept it a secret. It gave his words a little credibility, especially since she didn't even consider the possibility that he was the one who killed Aster.
"I was so scared that I hid for a long time before finally coming out. I still feel a chill run down my spine when I think about that moment," Eren said, raising his hand to show that they were still trembling.
"I didn't know where to go as I was worried that the monster might come for me as well," he quickly added, not giving Mist time to poke holes in his story.
While speaking, he kept stepping closer to Mist, in turn getting closer to her daughter who was standing right behind her.
"The only one who can protect me... The only one who can help me is you. In exchange for your protection, I am willing to tell you everything!" he said, justifying his reason for coming here.
