Historia Reiss

Christa Renz is a kind girl who puts herself out there and likes helping others.

Personality
She is a very useful person who enjoys helping other people, which makes other characters see her as some sort of god.

Background
As of the story, there's nothing concrete known about Christa's background. It is presumed she may be from the Trost District like Jean Kirschtein and Annie Leonhardt. After the arrival of the Colossal Titan and breaching Wall Maria, Christa had began her training in the military. Upon graduation she had placed 10th, a rank under Sasha Braus (this was due to Ymir leaving her the spot).

Current Plot
After the breaching of Wall Rose, Christa wasn't seen going into battle until Ch.6 when she was trying to help Armin overcome his dread of supposedly losing his friend. She helped Mikasa and the other trainees retake the supply room while the rogue titan kept the other Titans distracted. She didn't make an appearance again until Ch.21 when she had shown her Three Dimensional Maneuver Gear as the Military Police was looking for the one that killed the two captured titans.

Despite Christa's fears in facing the titans again after going through the same thing that Jean, Conny Springer and the others, she stayed put and became a member of the Scouting Legion. There, she helped save Reiner, Armin, and Jean by supplying a horse after they were stranded from an encounter with the Female Titan.

She was seen up on the trees baiting the titans and preventing them from entering the forest as the Scouting Legion attempted to capture the Female Titan. After this she wasn't seen again until Chapters 34 and 35 when the Haired Titan attacked with the other titans.

In Ch.37, Pastor Nick revealed that to the members of the Scouting Legion that Christa may know about the walls having titans inside them because of her family, and that she went under an assumed name after being caught in the middle of her relatives' dispute. It wasn't long until Eren and the others realised that Christa was often around Ymir.

In Ch.40, Christa remembers being with Ymir when they were helping Dazz in her hometown. She was confronted for living under an assumed name after being caught in the middle of a serious dispute between her relatives. Before transforming into a titan to fight the other titans attacking them, Ymir made Christa promise her to go back into living under her real name.

Trivia
It's possible that Christa Renz isn't her real name and it won't be revealed for some time.