"...I managed to hear my brother's last words before he really died...I was there when it happened...he told me to be strong for him...and then I was passed down his power..." Takahisa said, somewhat mentioning why he has a cold hatred towards Ayimu, the demon responsible for his brother's death.
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For a bit, Eren would see that Kaika was in this "dream" world, but she was unconscious and encased in a clear crystal, and he would see that some blue energy cord was connected to him and Kaika as if they were really linked together. Then, Eren would get brief flashes showing Kaika being stabbed by a dark shadow that many times that her body was like human swiss cheese, and so far as that Kaika's body was almost unrecognizable. Then...it all stopped. 

Just like that, Eren would then find himself in a town almost resembling the settlement in Wall Maria, and that he was with his gear too. Yet...it was certainly not the place he was born into and knew for a long time....