Hello!
Ref: https://www.kobo.com/pt/pt/ebook/attack-on-titan-before-the-fall-5-2
The story takes place in an undetermined future, where the human race was almost wiped out by the mysterious Titans. The Titans are humanoids of enormous stature (between 4, 15 and even 60 meters) that apparently are not interested in any form of life other than human.
To escape the titans, the man-eating giants, humanity took refuge in cities surrounded by massive walls. When they attack again, Eren Yeager joins the fight in an attempt to combat these evil creatures.
@criptomaster