This page contains information regarding Star Trek: Lower Decks, and thus may contain spoilers.
T'Lyn was a Vulcan female active during the mid-24th century who served aboard the Vulcan cruiser Sh'vhal until 2381. In that year, her crewmates had come to see her as "unstable" due to her tendency to act on factors other than logic, such as instinct and "gut feelings."
T'Lyn enhanced the Sh'vhal's long-range sensors by implementing personal algorithms, even though her assignment has been to monitor tertiary impulse systems. When the enhanced sensors detected metreon particles in system 7743.8, she reported the anomaly and the ship changed course to investigate. However, T'Lyn was ordered to spend two days in meditation due to her behavior.
The metreon emissions had been caused by a varuvian bomb detonated by Pakleds, and the Sh'vhal discovered the Pakled ship Pakled and the Klingon Bird of Prey Che'ta' attacking the USS Cerritos, a Starfleet vessel. The Sh'vhal intervened and took fire from the Pakleds and Klingons, damaging its shields. T'Lyn offered her captain a regenerative shield amplifier she had developed as a personal project. Though the protocol was untested, he implemented it, and shields rose to 120%. The Che'ta' broke off its attack, and the Sh'vhal helped the Cerritos drive off the Pakleds.
T'Lyn's captain noted that her actions had likely saved the ship. However, citing her lack of emotional control as a liability, he informed her that she would be transferred to a Starfleet vessel. Over her objection, he informed her that his decision was final. (LD: "wej Duj")