Titans (Attack on Titan)

The Titans (巨人 Kyojin) are the main antagonists of the anime/manga series, Shingeki no Kyojin, known in the western world as, Attack on Titan. Within the Attack on Titan universe, these human-esque monstrocities had nearly brought forth the extiction of the entire human race, with most of the world having been lost and forcing the remaining human beings to retreat inside the confined walls of a massive city state.

Much like the Romero Zombies of modern day horror fiction, Titans are hinted to be an off-shot of the human race now cursed to forever devour the rest of humanity. This was due recent chapters of the series reveals that their nature are almost same with Titan Shifters albeit their human bodies within their titan's nape are crushed and partially assimilated.

Physical Appearance and Charcateristics
Titans are creatures closely resembling human beings, but with various deformities, ranging from either over/under-sized heads and limbs, massively fat stomachs, or even skeletal frames. As the species' name would imply, titans dwarf over any human being. All titans keep their eyes constatly opened, their mouths posses lots of molar teeth used to grind human flesh. Titans possess no visible reproductive organs, thus it is unknown how they keep increasing their numbers. Each titan possesses unique facial features and hair style, much like any individual person. Strangely, despite their large size they are unnaturally light, with humans of average strength able to lift up their body parts without trouble. They also produce a high amount of heat and emit steam to control their body temperature. Due to lacking a digestive track, they don't require eating of humans to survive, instead they can absorb sunlight like a plant does. Titans also possess a high amount of regeneration which allows them to survive dismemberment, disemboweling, and decapitation while the back of their neck is undamaged. To exploit their weakness, the Three Dimension Gear were developed to target the nape of their neck.

Titans have several size variants:
 * Three Meter Titans: The smallest type of Titan. Due to their smaller stature, they are the weakest of the Titan types. Even farm equipment can gravely damage if not kill them, as Christa demonstrated. However, this also makes them the fastest of the three types.
 * Ten Meter Titans: The most common type of Titan. They are medium sized in the grand scheme of things and can smash through buildings and are virtually immune to gunfire. Titans of these size require Three Dimension Gear to kill.
 * 'Defiant' Titans: These are an abnormal type of titan, which can range from being smaller than the Ten Meter Titans (up to 5 and 7 meters) to 13 meters tall. Deviant Titans are also unique, they are far more active than other Titan types (not including Titan Shifters) and many possess agility other Titans lack, or speed or skills that other Titans lack. Ymir is a member of this subtype.
 * 15 Meter Titans: Formally the largest type of titan known, they were also the most dangerous. A single 15 Meter Titan can take down an entire squad of troops without effort, smash through two story buildings, and even withstand cannon fire due to their rapid regeneration. When Eren transforms, he becomes a unique 15 Meter Titan.
 * Armored Titans: As the name suggest, these titans can produce crystalline armor. They usually rank around the same size of the 15 Meters, and are more muscular built. They also possess a high amount of speed and durability with cannonballs just bouncing off their armored bodies. The only areas that aren't armored are their joints which are vulnerable to attack. Reiner Braun is the only known member of this subtype.
 * Beast Titans: As the name suggest, these are titans that have animalistic appearance. They are also larger than the 15 Meter Titans, reaching a height of 17 meters. Unique to even Titan Shifters, the Beast Titans are highly intelligent, able to communicate with humans by speaking their language. They also have the ability to control other Titans and freely turn people into Titans. The Beast Titan is the only known member of this subtype.
 * Female Titans: Another new type of titan, as the name suggest these are titans with female characteristics. They range from 10 meters to 15 meters in height. They are also able to form temporary crystalline armor to protect themselves and have shown far greater agility than their male type counterparts. Annie Leonhart is one member of this subtype, with Connie's mother being another member.
 * Colossal Titans: The largest and strongest type of titan, they range from 50 meters to 60 meters in height. A 60 meter tall Titan was the one which ended the era of peace which humanity was enjoying behind the walls by destroying the gate of Wall Maria with a single kick, creating a shockwave that destroyed the first few districts that were near the gate. They are also able to produce superhot steam as a defensive mechanism due to their size hampering their movement. Bertolt Hoover is one member of this subtype, with hundreds of them hidden in the very walls themselves.

Behaviour and Goals
Some humans such as Eren Jaeger, have the unique ability to summon and control a Titan body. While in this form, the human's normal body rests in the weak point at the base of the neck, connected via masses of muscular tissue, indicating a connection between the sentient and feral Titans. Certain Titans are noted to be Deviant-Type (奇行種 Kikō-Shū), acting in a way that is not normal for Titans, such as not eating humans directly but acting in a way to help their fellow Titans and easily controlled by Titan Shifters that have ability to control regular Titans.