Within Attack on Titan, Sasha Braus' characterization centered around her providing a sense of comedic relief through the heavier themes of the popular anime. As such, she never reached main character status, and didn't receive the same depth and development as some of her counterparts. While Sasha did have an inspiring character arc, it's not comparable to Eren Yeager or Reiner Braun, so she became known as more of a side character.
Source：https://www.cbr.com/aot-sasha-potential-shonen-protagonist/
