First, she recovers from her Villainous BSoD when she discovers that Sayaka's still alive and carry her to the nurse's office to save her life.
Then, she makes a run to the court room to stop Leon from getting executed, stopping the baseball launcher in the process and daring Monokuma to check the nurse's office to confirm Sayaka's survival.
After Mukuro ruined the first trial, her insane sister confronts her about the incident, Mukuro stands defiantly against her sister, reassuring her Redemption Quest and solidifying her HeelFace Turn. After spending years submissive to her sister, she finally Grew a Spine and has found a new purpose in life!
Mondo smashing his head into a wall so that Taka will go to help Chihiro
Chihiro finally snapping in rage at a few points and spewing out rather passionate words about how she feels about the whole situation with Byakuya after the Trial, and Mondo and Taka both take great pride in her for her growth into a stronger person.