Kai Zimmer

Kai Duemmel (カイ・ヅンメル) is a recruit of the Survey Corps. He appears in the light novel Attack on Titan: Before the Fall 3 and the manga series Attack on TItan: Before the Fall.

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 Training Corps.

Personality
Ambitious and brave, Kai shows a desire to join the Survey Corps with his squadmates. He exhibits bravery and wishes to fight against Titans for the sake of humanity, just like his hero Jorge Pikale.

Restoration of the Survey Corps arc
During a training session, Kai and his other squadmates 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.

Some time 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.