Attack on Titan

Attack on Titan (進撃の巨人 Shingeki no Kyojin?, lit. "Advancing Giants") is a Japanese manga series written and illustrated by Hajime Isayama, which is set in a world where the remains of the human population live inside cities surrounded by enormous walls due to the sudden appearance of the Titans, gigantic humanoid creatures who devour humans seemingly without reason. The story centers around the life of Eren Jaeger and his adoptive sister Mikasa Ackerman, whose lives are changed forever after the appearance of a colossal Titan brings about the destruction of their home and the death of their mother.
An anime television series debuted on April 6, 2013, on MBS. A live action film adaptation is also in production.
One hundred years prior to the beginning of the story, giant humanoid creatures called Titans (巨人 Kyojin?) have forced humanity to devolve to a medieval level of technology and to retreat into a system of concentric Walls (ウォール Wōru?) known as Wall Maria (ウォール・マリア Wōru Maria?, outermost), Wall Rosé (ウォール・ローゼ Wōru Rōze?, middle), and Wall Sina (ウォール・シーナ Wōru Shīna?, innermost). Inside these walls, humanity lived in peace for one hundred years. But in the beginning of the story, a sudden attack by a gigantic sixty-meter Titan and a smaller Titan covered in armor plates causes the outermost wall to be lost, forcing mankind to abandon the land between Walls Maria and Rosé, leading to famine and turmoil.
Little is known about the Titans, giant creatures that are usually between 3-15 meters tall with a few exceptions. The Titans attack and devour ordinary humans on sight instinctively, although apparently they do not need to feed to survive, as they do not prey on other animals, even with the abscence of humans, surviving by absorbing sunlight. They have hard skin and regenerative abilities, and can only be killed by a deep incision on the base of the neck. This weakness led to the development of the 3-D Maneuver Gear (立体機動装置 Rittai Kidō Sōchi?), allowing humans to navigate quickly in a three-dimensional space to access the Titans' weak point. Though it allows great mobility to a skilled user, it carries a large risk of overtaxing the muscles, thus a special physical conditioning and sense of balance is necessary to master it.