Rico Brzenska

Rico Brzenska (リコ・ブレツェンスカ) is the Squad Leader of the 1st Division Elite Force of the Stationary Guard. She is the sole survivor of the elite squads assigned to protect Eren during the liberation of Trost District. She does not trust Eren and still views him as an unstable threat.

Story
Rico is first seen in Episode 9 when Eren, Armin, and Mikasa cornered. Then in Ch. 13 she observed Eren in Titan form going berserk. She hastily signals mission failure, but Ian convinces her to continue. When Eren recovers, she, along with the rest of the elite squad, cut a path to the breach. At one point, when a titan converges on Armin, Rico rams her swords into its eye and Mikasa finishes it off. When the rock is finally in place, she observes that everyone else is dead and they are later rescued by Rivaille.

She also testifies against Eren at his trial in Ch. 19, convinced that he is a danger to himself and humanity.

Rico does not appear again until Ch. 38, when the Stationary Guard is deployed against the Titans which have mysteriously appeared within Wall Rose. Rico is in charge of the Eastern line of defense, where her squad lures Titans into cannon fire and she uses her Three Dimensional Maneuver Gear to cut their necks while they're disabled.

Trivia
In the anime, she appears to be bit more trust worthy of Eren than in the manga. The line about her concealing and lying to testify against Eren was never made, and she seemed rather ashamed or disgusted that she had to write in how he attacked Mikasa in the report.