Jean Kirschtein.

Jean Kirstein (ジャン・キルシュタイン Jan Kirushutain?) is a graduate of the 104th Training Corps, where he ranked 6th best. Jean hails from Wall Rose's Trost District, and joined the military hoping for a peaceful life as part of the Military Police Brigade, but later found himself joining the Survey Corps. He served as a commanding officer in the Survey Corps, leading a squad during the Raid on Liberio.

Jean is a young man with spiky, gray hair shaved into an undercut style, with the shaved portion being black. He has small, intense brown eyes, and is said to have the same vicious look in them as Eren does. Jean is of average height and muscular build, and has a scowl similar to Eren's but is said to have a long face (a "horse face"). He is often seen wearing the typical uniform of the Survey Corps worn with an olive-gray button-up shirt. After overthrowing the government, his hair appears slightly longer than before. His casual attire mostly consists of a white button-up shirt, dark pants, and a dark-brown vest. When concealing his identity, he also wears a cloak and fedora. Four years later, he has grown a goatee and his hair is now longer. He has also grown to be quite tall as an adult, standing at 190 centimeters. While infiltrating Marley, Jean wears a black Survey Corps uniform with anti-personnel vertical maneuvering equipment.

Jean has a blunt personality. He holds no restraint when it comes to speaking his mind, even when he knows it would not be wise to do so or when it could spark conflict. Jean is also pragmatic: he has a strong aversion to exposing himself to dangerous situations, and has openly admitted his desire to join the Military Police is due to wanting an easy and safe life. During his time as a trainee, Jean was extremely hot-headed, easily becoming frustrated and quick to resort to violence when pushed. Jean was also very cynical about defeating the Titans, believing that humanity had no chance against them. He openly mocked more idealistic individuals like Eren, and saw resisting the Titans as a hopeless cause. Despite his shortcomings, Marco describes Jean as a natural leader, able to understand others and assess situations well because of his flaws. Indeed, during the Battle of Trost, Jean proves capable of leading his fellow soldiers when they are left confused and leaderless, and rallies Armin and Reiner in an attack on the Female Titan, knowing that not fighting her would endanger the rest of the Survey Corps. His awareness and leadership capabilities were further displayed during the Battle of Shiganshina, when he took command of Armin's squad, and in Liberio when he led many of the 104th graduates to attack the Marleyan military. Over the years he gained great appreciation from Connie, who deems him capable of becoming a future leader of the Survey Corps.

After coming of age, Jean enlists in the military, joining the 104th Training Corps. On the day of his enlistment, Jean confidently admits his desire to join the Military Police and receives a headbutt from Keith Shadis for his trouble.

That night, Jean overhears Eren Yeager talking about his desire to join the Survey Corps and criticizes him for the decision, but apologizes after seeing that his words have upset Eren. As the trainees file out of the mess hall, Jean sees Mikasa and, immediately taking a liking to her, tries to talk to her but she immediately blows him off in favor of talking to Eren. Devastated, Jean develops a grudge against Eren.

The following night, after performing well during his first day of Vertical Maneuvering Equipment aptitude training, Jean is approached by Eren for tips on how to maintain balance, but Jean only ridicules him for his poor performance.

Over the course of training, Jean and many other trainees begin to slack off in all areas except those absolutely necessary to graduate in the top 10, including hand-to-hand combat lessons. On another night, Jean brags to his friends about his maneuvering equipment, joking that they shouldn't tell his secrets to others so he won't face extra competition for a spot in the top 10 graduates. His joke annoys Eren, who criticizes the idea of improving one's Titan-killing skills to get a military position further away from the Titans. As their argument escalates, Jean finally loses his temper and gets physical with Eren, prompting Eren to disarm him by kicking out one of his legs. Their fight is interrupted by Instructor Shadis, and Eren and Jean agree to finish it later. This motivates Jean to start taking his training more seriously.

Long ago, humans were just food for the titans. Until humans built three giant walls around their country. Wall Rose is the second outermost Wall following Wall Maria. It was breached by the Colossus Titan 5 years after the fall of Wall Maria, but the breach was later sealed by military efforts of the three branches and help from the Attack Titan. Wall Sina is the innermost Wall protecting the kingdom where the king and other civilians reside. The cities of Wall Sina are protected by the Military Police serving under the king. The underground is poorer and more prone to criminal activity. Wall Maria is the outermost Wall of the human kingdom. Like the other Walls, Wall Maria is approximately 50 meters in height. Five years ago, it was breached, after a century of peace and prosperity, and was lost to the Titans. The human military against the Titans is divided into three divisions: the Survey Corps, which explores the areas outside the Walls; the Garrison, which patrols and maintains the Walls, preventing Titans from entering the Walls in case the gates are breached, primarily to delay and distract the Titans; and the Military Police, high-ranking soldiers who serve as personal guards for the King and maintain order within the Walls. The Survey Corps (調査兵団 Chōsa Heidan?) was the branch of the Paradisan military most actively involved in direct combat with and study of the Titans. Due to their constant expeditions, the Survey Corps' soldiers were the most proficient in the use of the 3D Maneuvering Gear and the Anti-Personnel Spatial Maneuvering Device. Despite little success from their activities, the members of the organization still symbolized the "hope of humanity", and their insignia was known as the "Wings of Freedom". The Survey Corps' goal was to someday change the world and take back what was taken from humanity.

Garrison (駐屯兵団 Chūton Heidan?) is the most numerous, but also the least qualified (except for elite units) branch of the military. Due to the high mortality rate of the Survey Corps and the high competition for recruitment into the Military Police, people most often prefer it. The main task is to protect the Walls during an attack by the Giants and the subsequent evacuation of the civilian population. Secondary: organizing order, patrolling, repairing defensive structures. In the battle for Trost, the Garrison fighters not only defend the walls, but also independently clear out the captured areas. It was they, along with the cadets, who participated in the defense of Trost, only then the Survey Corps cleared out the city. The Military Police (憲兵団 Kenpeidan?) is the most prestigious branch of the military. This is because their job allows them to live within the inner walls, in safety. The Military Police have a lot of resources, and their power is greater than that of the Garrison and the Survey Corps. In reality, the Military Police have a complete lack of supervision and discipline, abuse of power can be seen everywhere, they have a bad relationship with the Garrison and almost hateful with the Survey Corps. Only the top ten cadets can get into this branch of the military, but judging by the conversation between Boris and Hitch, there are other, illegal ways to get into the police. Most titans are pretty stupid, but despite this, killing even one titan is quite problematic. Only one weak spot has been discovered in titans - the neck. If you cut even part of a titan's neck, it dies immediately.