Sito Jaxa was a Bajoran Starfleet ensign who overcame a disgrace at the Academy, served on the Enterprise-D and was killed on a secret mission in 2370.
Sito Jaxa was a member of Nova Squadron, the elite cadet flight team at Starfleet Academy that included Wesley Crusher. When a forbidden maneuver killed one of the team, the cadets tried to cover up what had happened. After the truth came out, Sito was allowed to continue but carried the mark of that scandal on her record.
Picard later backed her posting to the Enterprise-D, giving her a second chance. Worf tested her harshly to see whether she would stand up for herself, and she rose to the challenge, earning his respect and a strong reputation among the junior officers. She then volunteered for a dangerous covert mission to return a Bajoran agent into Cardassian space in a disguised escape pod. The pod was later found destroyed near the border, and Sito was presumed dead.
Sito's story shows the pressures faced by junior officers and the real cost of Starfleet missions, and her loss left a deep mark on the crew.