The story initially centers on Eren Yeager, his adopted sister Mikasa Ackerman and childhood friend Armin Arlert, who join the military to fight the Titans after their home town is invaded and Eren's mother is eaten.
Walls: Walls are built up in order to keep Titans outside. However, a few of them could do damage to that wall.
Wall Maria: Wall Maria is the outermost wall of the human kingdom.
Wall Rose: Wall Rose is the second outermost Wall following Wall Maria.
Wall Sheena: Wall Sheena is the innermost Wall protecting the kingdom where the king and other civilians reside. The cities of Wall Sheena are protected by the Military Police serving under the king.
The 104th Training Corps (第104期訓練兵団) is the only graduating class introduced in the series and the Southern division contains nearly all of the central characters including Eren and Mikasa. Its goal is to train soldiers with battle skills and provide reinforcements for other Corp during battle.
The Survey Corps (調査兵団) is the branch of the Military most actively involved in direct Titan combat, Titan study, human expansion, and outside exploration. They have the best soldiers (not to be compared with the Top 10 who joins the Military Police Brigade), and are the most skilled in using the vertical maneuvering equipment.
Captain Levi is one of the elite soldiers in this Corp.
The Vertical Maneuvering Equipment (立体機動装置) is a set of equipment developed by humans that allows great mobility when facing the Titans in combat. The equipment allows the user to fight in a 3D space instead in a 2D one.
Mikasa and Eren witnessed their parent's deaths caused by the Titan. Eren sweared that he would kill as many Titans as possible. So he enlisted in army and Mikasa went with him so that she could protect Eren as she sweared.
Giant Titan came out, and he broke the first wall, allowing hundreds of Titans enter the town. Soldiers in Training Corp, including Eren and Mikasa, are ordered to fight against Titans.
Human suffered a great loss. The first wall was down, Eren and Misaki were forced to retreat to the second wall. Their peaceful life has come to an end.
In the battle, Eren found out that he could shift into a Titan and became invincible. That is his superpower, and he became one of the "Titan Shifters"
In the investigation after the battle, Eren and Mikasa found out Annie, another Titan shifter, is responsible of releasing that Giant Titan. They resorted this to the Survey Corp and Military Police, and they all decided to take action to arrest Annie.
Eren, Mikasa and soldiers went to arrest Annie. But she turned herself into a Titan to fight them. Eren also turned into Titan as a response and they had a hard time fighting against each other. Eren was heavily wounded by her skillful combat ability.
Mikasa and Levi came just in time and joined the battle. With the help of them, Eren defeated Annie and she was sealed in a huge piece of ice.
Eren was saved by his elder sister. They went back to Training Corp safely.
They joined in Survey Corp after graduation and Captain Levi became Eren's tutor and he also taught Eren how to control his superpower.
Eren knowed that it is also important to use wisdom and strategies in battle as well as people's daily lives instead of only use power and force. And he also learned that only family members are the closest people for everyone in the world.
Storyline is attractive and moving: it shows the loss of loved ones, separation and reunion of families, and also, it shows how brave and responsible the soldiers are when people are in danger.
Imagination: the Titan, the Walls, military equipment.