Of course, the immediate follow-up question is: How is Mariner still an ensign in her early 30s? Fans of “Lower Decks” will hastily answer that Mariner is deliberately subordinate, and disobeyed orders as a matter of course. She has no interest in advancing in her career, happy to stay an ensign indefinitely. At the beginning of season 4, Mariner was promoted to lieutenant, junior grade, something she didn’t want and is struggling to accept. It wouldn’t be until the last episode, “The Inner Fight,” that Mariner would reveal her motivations for staying an ensign … and it has everything to do with the flashback to “The First Duty” 13 years ago.
It seems that Mariner, when she was an eager, first-year academy student, was close friends with a Bajoran student named Sito Jaxa (Shannon Fill). Sito was involved in a scandal at the Academy wherein a hotshot friend of hers, Nick (Robert Duncan McNeill), convinced her and a few others — including Wesley Crusher (Wil Wheaton) — to engage in a dangerous and unauthorized flight maneuver during an airshow. The flight was incredibly dangerous, and a classmate was killed. Sito was involved in the subsequent cover-up, but all the students were eventually exposed and held back a year.
Sito eventually served on the Enterprise while Mariner was still at the Academy, but was killed in a dangerous spy mission (see the episode called “Lower Decks” from February 7, 1994). Sito’s death shook Mariner, and she started to become disillusioned with Starfleet’s structure-based ethos. Her response was to defy authority, happy to be an irascible troublemaker with a dead-end career.
By age 31, Mariner is still a low-ranking officer eager to sow chaos in defiance of the system that killed a friend she looked up to.