Kai Zimmer

Kai Zimmer (カイ・ヅンメル) is a recruit of the Survey Corps.

Appearance
Kai is a young man with brown eyes and hair, with the hair on the back of his head trimmed down much shorter. He wears a white shirt underneath the traditional uniform of the Survey Corps.

Personality
Ambitious and brave, Kai shows an early desire to join the Survey Corps with his squad-mates. He exhibits bravery and wishes to fight against Titans for the sake of humanity, just like his hero Jorge Pikale. Kai can also often speak without thinking his words through, causing some to view him as inconsiderate and rude; despite this, he holds his friends and allies in high regard and does not hesitate to try and defend them whenever they are threatened.

Restoration of the Survey Corps arc
During a training session, Kai and his other squad-mates come across an unconscious teen who washed up along the banks of a river. They take him to a nearby cottage for him to heal; due to being trainees at the nearby academy, they are only able to visit at night and do their best to help the teen recover. Roughly a week after they find him, Kai is informed by his squadmate Rosa that the teen is awake; him and his friends decide to return that night and learn the teen is named Kuklo. When Rosa says Kuklo is part of a mystery group that is developing a weapon to defeat Titans, Kai seems interested and expresses his overall desire to join the Survey Corps like Jorge Pikale; when he hears from Felix that Jorge will be there in a few weeks, Kai becomes excited at the thought of finally meeting his idol. Kuklo, after seeing Kai and the others' determination, offers to put in a word for them but cautions they will need to be serious about training. Kai becomes slightly unnerved when hearing Kuklo discuss several expeditions he took part of that resulted in the deaths of countless Survey Corps soldiers; nonetheless, Kai, along with the other recruits, promise to do their best.

A week goes by and Kai, Rosa and Ivo return to the cottage to discover two members of the Military Police approaching it. Fearing that Kuklo will be discovered, Kai calls out to them and nearly gets shot. After being accused of harboring fugitives, Kai attacks one of the MP's after he sees Rosa getting slapped aside. As a result, Kai gets hit in the face with the butt of a rifle, briefly stunning him. After Hugo and Felix arrive with Jorge Pikale, the Military Police members back down. After finding nothing, the two leave after apologizing. When Kuklo flies out of a nearby tree, Kai is stunned to see it in action and hearing how Kuklo used it to escape. While Kuklo and Jorge speak in private, Kai briefly entertains the notion of eavesdropping on the conversation but Rosa and Felix warn that it would be grounds for his eligibility to join the Survey Corps rescinded.

Sometime later, Kai and his friends hear about a new training program for Survey Corps recruits and volunteer to take part. Along with Rosa, Kai notices Kuklo being addressed by a different name by Captain Carlo Pikale, but is quieted by Felix. As they start the first exercise, Kai is surprised by how heavy the knapsacks they must carry are, with Felix realizing they are filled with sandbags. After several hours, Kai and the others are exhausted but continue to keep going. After Rosa passes out, the others discuss what to do. Kai volunteers to carry Rosa, but nearly falls over himself. Hugo decides to carry Rosa instead, with Kai taking two of the knapsacks. Later that night at the mess hall, Kai and the others are eating when they start to hear several other trainees mocking their performance earlier. Kai starts to get up, but Ivo prevents him with a look. Eventually, Kai starts to talk back when he suddenly sees Felix stand up and punch the trainee mocking them in the face. Kai joins in and a fight erupts in the mess hall, earning all of them a night in the guardhouse as punishment.

As the training period goes on, Kai and his friends show much progress and learn that the program is being altered once again; Kai congratulates Ivo when he becomes the first one to successfully stay balanced on the aptitude training device designed to work on balancing. Kai is among those present when a monitor from the Military Police, Xavi Inocencio, arrives and manages to effortlessly stay balanced on the device as well. The following day, the trainees are informed that they will be traveling to the Wall; Kai makes a joke but is quickly silenced by Jorge glaring at him. Arriving at the edge of the Wall, Kai is surprised by how large the Wall is and climbs up to the top of the Wall along with the others. After reaching the top, Kai and the other trainees notice the Titans lumbering just below them and expresses shock and disgust at the sight of them. He takes note of the destructive powers of the cannons on the Wall, along with how the Titans regenerate at a quick rate. After returning to the Training grounds, Kai asks Ivo and Hugo if they are reconsidering whether or not to leave after witnessing the Titans; he is glad to hear they both are staying and mentions that his resolve to fight has not changed either.

During the second round of the aptitude training, Kai manages to pass along with Rosa. While offering that night to toast on their success, he is quickly (and sternly) reminded by Rosa that Felix failed the test again. He overhears Rosa's apology for her rude behavior recently and after Felix reveals his reasons for fighting the Titans, notes that everyone is back on good terms; he then joins Hugo and Ivo in teasing Felix on his apparent feelings for Rosa. The next day during their training with the vertical maneuvering equipment, Kai sees Rosa use the device flawlessly and cheers her on with Ivo, Hugo and the others. After Felix passes as well, Kai helps him put on the equipment and is shocked at the sight of the Titan training dummy; he becomes resolved after hearing from Carlo and Kuklo that it will be used as part of the training to simulate an actual Titan.

After he witnesses Rosa fail due to her equipment being sabotaged, Kai hears during dinner that the maintenance room will be locked down in a few days. Due to that being where the equipment was located when the sabotage occurred, Kai proposes to his friends that they try and track down the person responsible themselves; Felix immediately agrees to the plan and both Ivo and Hugo voice their support as well. The next day, they are surprised to see Rosa back from the infirmary. Despite Rosa inquiring, Kai does not reveal their plan to track down the ones behind the sabotage, but both him and Felix unintentionally cause Rosa to storm off. That night, they skip dinner and make their way to the maintenance room. As they ponder what to do, they fail to notice someone else spying on them too. Soon, they spot movement and head towards the outer wall; Kai has Hugo boost him up to the window in order to get a better look when Kuklo appears, and questions why they are out; despite not approving of their actions, he allows Kai and the others to join him. After they reach the maintenance room, Kai is surprised to see Xavi inside, along with the true culprits: the trainees they fought who had insulted Rosa earlier.

Due to disobeying orders, Kai and his friends are sent into the guardhouse as punishment; when Felix mentions that they should not complain about being punished, Kai retorts that Felix has been in there three times already and is used to it. He then muses what could have been the driving cause for the trainees to damage Rosa's equipment and cause her to get injured. He ponders if it was due to the earlier fight, but both Ivo and Felix think they were being ignored and left behind in favor of the special training class.

Survival Expedition arc
At the end of the three month training program, Kai along with his friends and all the other trainees are accepted into the Survey Corps. Kai is put into a group consisting of the special training members and is surprised that Rosa is selected as the group's Team Leader; that night, Kai calls for a toast and immediately orders another glass of ale after finishing his mug. He notices Kurz not partaking and begins to needle him over it; when Kurz looks away, Kai secretly adds in some alcohol and starts laughing when Kurz unknowingly downs it in one gulp. After both Felix and Kurz express a desire to become a Team Leader someday, Kai joins in as well and then is among those that ask Rosa to give a rousing speech to her new subordinates.

Kai rides out with the rest of team ten as the expedition starts several days later, stopping at an oasis five kilometers beyond the Wall. After refilling his canteen at the lake located there, Kai is summoned with the others due to the presence of a red signal flare. Soon, it begins to rain and team ten loses their bearings due to the signal flare disappearing; they regroup with Captain Simon Barna and team nine, coming across the remains of team seven and eight. Kai and the others surmise that a ten meter Titan was responsible and gives a vote of confidence when Rosa is asked whether to continue the expedition.

Upon arriving at the ten kilometer Survey Corps checkpoint, Kai is alerted that there are Titans nearby. He coordinates with Ivo and is able to slice the Titan's heels with their blades. When Rosa and Cardina land the killing blow and slice apart the Titan's nape, Kai immediately starts to celebrate how they managed to kill a Titan; he becomes upset that Xavi was not present, but remains confident they can do it again. After Felix is injured saving Rosa from another Titan, Kai quickly organizes efforts to gather the horses and prepare for another attack on the Titans. Another red signal flare is spotted and they quickly get into formation.

Kai immediately engages the approaching five meter Titan and works in coordination with Hugo, launching himself high above the Titan. He brings his blades down and slices apart the Titan's nape, avenging Felix; however, the sudden dissipation of the Titan's body causes Kai to lose his balance, landing across Hugo. He stares at the location of the ten meter Titan before getting his attention drawn towards some rubble; he is relieved to see that Felix was saved due to the actions of Simon.

It is presumed that after the return of the surviving soldiers from the expedition, Kai took part in the ceremony that saw Carlo Pikale promoted to the official commander of the Survey Corps and stayed on as a member of the newly reformed military branch.

Relationships

 * Jorge Pikale - Kai idolizes Jorge Pikale and sees him as his main role model. He has a strong desire to join the Survey Corps to fight alongside Jorge in defeating the Titans outside the Walls.
 * Rosa Carlstead - While friends with Rosa, he can often times get on her nerves due to his demeanor. Despite this, he is protective of her and will put himself in harm's way to make sure she is safe.
 * Kuklo - Kai was one of the first of his squad-mates to accept Kuklo after hearing that he was working with the Survey Corps on a device to fight against the Titans. Seeing Kuklo use the device in action helped motivate Kai to work hard and achieve his dream of joining his hero Jorge in the Survey Corps.