(why is it hard to lose someone) Attack on titan

When 4 friends (Zainu, Zoni, nobara, and Jennie) we're having a normal day in wall maria helping eren and mikasa with woods... just running in the field... helping Carla... and suddenly the beautiful world that was snatched from them... or just the beautiful they thought was beautiful.... but actually it was hell? let's go on the journey of these 7 friends... who will live? who will lost life? who will be the betrayer? and who will be the hurt? who will change?.... so many questions yet to be answered?...