In an alternate timeline, Lieutenant Natasha Yar was security chief on the battleship USS Enterprise-D during the Second Federation-Klingon War. In this timeline, Yar joined the crew of the Enterprise straight from Starfleet Academy, considering herself lucky to have been given an assignment aboard the vessel.

In 2366, the Enterprise-D encountered a temporal rift, from which emerged the USS Enterprise -C. During the course of repairs to the displaced vessel, Yar worked closely with the Enterprise-C officer Richard Castillo and developed romantic feelings for him. She also became aware that Guinan was slightly uncomfortable around her, and forced Guinan to reveal that she had died a senseless death in the true timeline. After the captain of the Enterprise-C, Rachel Garrett, was killed in a Klingon attack, Yar requested transfer to the Enterprise-C. She realized it was a virtual suicide mission, but she was very concerned about Castillo and also wanted to somehow change her meaningless death into one which counted for a cause. After gaining Captain Picard's grudging approval, Yar assumed the tactical position on the Enterprise-C and successfully returned to Narendra III with the ship. Her actions allowed the vessel the minutes it needed to restore history to its correct course - preventing the war from ever taking place. (TNG: "Yesterday's Enterprise")
Castillo and Yar

While the Enterprise-C was destroyed, some of the crew members were captured, including Yar. The Romulan general who oversaw their capture became enamored of her, and spared the lives of the remaining crew in exchange for Yar becoming his consort. One year later, she gave birth to a daughter, named Sela. Yar was still not completely satisfied with remaining with the Romulans and when an escape opportunity presented itself, she took it. She took her daughter, then four years old, but Sela cried out for fear of being separated from her father and her life. Yar was caught and executed, and Sela claimed that the Human part of her died that day as well.

The events surrounding the Enterprise-C remained unknown to the Federation until 2368, when Captain Picard and the Enterprise-D encountered Sela along the Romulan Neutral Zone. Her story was corroborated by Guinan. (