Jean Kirstein

Jean Kirschtein (ジャン・キルシュタイン) is a graduate of the 104th Trainees Squad and graduated in the top ten of his class. Being Eren's rival and often at odds with him, he serves as the series' foil character.

Personality
Jean most notable trait is that he speaks whatever is on his mind, even when he knows it would not be wise to do so or that it would cause conflict. This, along with their differing viewpoints, is the cause of his conflicts and rivalry with Eren. Nonetheless, he is an honest individual.

History
As part of the 104th, he ranked in the top ten of its graduates, placing just under Eren Jaeger and coming in at sixth. After the graduation ceremony, he got into an altercation with Eren, who he seems to be very competitive with. As a self-described realist, his ideas and outlook initially conflict with Eren's more idealistic views. He states that he became part of the top ten so that he could join the Military Police and live within the Inner District in relative safety and comfort.

After the second attack of the Colossal Titan, he, like many others, was eventually sent to the front to deal with the titans that had entered the city. However, due to the supply shortage, he was unable to fight at first. With the arrival of Mikasa, he and the rest of the group rush towards the HQ to resupply. When Mikasa runs out of gas, he takes the lead. When another soldier runs out of fuel, he takes advantage of the distracted titans and orders the remainder to finish the remainder of the trip. He second guesses this decision when he realizes that he and the group only made it because he took advantage of the deaths of his teammates.

When he sees the resupply team, he strikes one in anger, telling them they are responsible for the soldiers being killed. Soon after, Mikasa, Armin and Conny arrived with the help of the rogue titan. Still having to deal with the titans in the headquarters, he was in the second group in Armin's plan to clear the supply room.

After resupplying, he stayed back with Reiner and Annie. After Reiner suggested helping the rogue titan out, Jean was hesitant, as they had just barely escaped with their lives and he was unwilling to risk it again for a titan. Fortunately, they didn't have to, when the titan broke itself free in order to attack another titan, collapsing soon after. He ended up being one of the first people to know about Eren's titan transformation, when he emerged from the fallen rogue titan.

It was revealed that during another altercation in Ch.17, Eren upon learning that Jean's behavior was similar to his own at one point, becomes a soldier. After learning one of Annie's techniques in hand-to-hand combat, he uses it on Jean and confronts him for his actions. Against his own wishes and his fear, Jean joins the Scouting Legion when he should've left with his other classmates. In Ch.31, he was chosen to pose as Eren because both have similar bad attitudes and eyes.

In Ch.34 at Eren's bedside, Jean finally learns about Annie being the Female Titan from Armin and she's encased in a crystal to avoid interrogation. He also finds out that about the titans similar to the Colossal Titan inside the Walls being used due to their hardening abilities. Jean and Armin heads down to the meeting between Commander Irvin Smith and the head of the Military Police.

Jean reappears in Ch.45 and is outraged when he learns of Reiner and Berthold's traitorship and their secret correspondance with Annie. He also learns about Ymir being a titan and that both she and Eren are taken hostage. Outraged and determined to stop his traitorous teammates, Jean readily takes his stance with the Scouting Legion, Military Police and Stationary Guard.

Relationships

 * Eren Jaeger - Eren and Jean share a very pronounced rivalry. Eren finds Jean's initial goal of living a safe, privileged life in the police force to be cowardly and disgusting. Jean on the other hand, finds Eren's eagerness to join the "suicidal" Scouting Legion to be idiotic. Though the two often engage in fist fights, they could also be considered friends of sorts. It is hinted that Eren's closeness to Mikasa and Jean's subsequent jealousy partially fuels the two's rivalry.
 * Mikasa Ackerman – Jean seems to have a crush on Mikasa. The moment he met her, Jean became nervous and commented how her "black hair is beautiful." Jean is somewhat resentful of Eren because of the attachment Mikasa has with him.