The Timeless Child storyline saw the introduction of Tecteun into the Doctor Who Universe. This storyline in the most recent season of the show changed the history and the future of the Time Lords and The Doctor, and revealed the part that Tecteun ultimately played in their creation.
As part of Gallifreyan history, an engineer of the existence of the Time Lords, and the head of Division, Tecteun went from being a one-off character to suddenly redefining what it meant to be The Doctor and a Time Lord. Knowing what we know about Tecteun now and the fact that Russell T. Davies is returning to the show, what kind of scope is there for the character's return?
Tecteun's Role So Far
First introduced during the series 12 finale "The Timeless Children," Tecteun is introduced to both The Doctor and the audience through The Master. The Master takes The Doctor to the Matrix, the sum of all Time Lord knowledge, to show her the truth behind both her own and her people's history. It's revealed that the indigenous people of Gallifrey were actually the Shobogans, one of whom was Tecteun.
As the people's first space explorer, Tecteun journeyed out into the stars where on one planet she discovered a young girl through a portal that led to a different universe or dimension. Tecteun took the child back to Gallifrey where, when she was older, she suffered what should have been a mortal accident. However, instead of dying, the girl regenerated. This simple accident prompted Tecteun to begin her experiments on the child, ultimately extracting the ability to regenerate from her adopted child after forcing her to regenerate multiple times and gifting it to the rest of her people. This is how the Time Lords began.
Through this revelation, The Doctor discovers that she was the child found by Tecteun and that both she and The Doctor once worked with the clandestine Time Lord organization Division. Division exists outside of Time Lord society, interfering with time as they see fit, and evades their rules by staying in the space between universes. The Doctor has no memory of this, or of her lives before becoming the First Doctor.
From this point, Tecteun isn't seen again until Chapter 3 of Doctor Who: Flux, "Once, Upon Time." Initially portrayed as an older woman named Awsok, it is revealed that she is in fact the third incarnation of Tecteun. Awsok blames The Doctor for The Flux and tells her to give up, but refuses to elaborate on the reasoning behind the fault laying at The Doctor's feet.
Awsok doesn't show up again until Chapter 5, "Survivors of The Flux," where her true identity is revealed to The Doctor. Awsok explains that she is Head of Division and that Division incorporates members of many species and extends across time and space. Awsok explains that they are in between universes and that The Flux is destroying universe one, leaving universe two the only option. She also reveals that she blames herself for the way in which The Doctor meddles in the universe, and ultimately Division's plans.
After revealing herself to be Tecteun, she tells The Doctor that The Flux was created because of her, and explains that she and Division wiped her memories of any previous lives she had before becoming The First Doctor. Tecteun offers The Doctor an ultimatum: return to her original universe and die with her friends, or regain her memories and join Division. The Doctor refuses her offer, but before anything else can be explained, Azure and Swarm arrive at the Division ship and state their intent to get revenge on the organization, beginning by disintegrating Tecteun.
Will We See Her Again?
Having examined Tecteun's brief but pivotal appearance in Doctor Who, is there scope for her character's return? Considering the nature of her character and that of the show, the answer is yes. Death and disintegration don't mean much in a show that plays fast and loose with the laws of space and time.
There are plenty of opportunities for Tecteun to return, either in the past or the future. At the end of The Flux saga, the fob watch that contained The Doctor's memories was secreted away in the TARDIS. The future opening of this watch could lead to flashbacks that feature Tecteun, or even leave a gateway open for a spinoff that shows what she and The Doctor did at Division before the erasure of The Doctor's memories.
The real question regarding Tecteun is whether her existence will even continue once Russell T. Davies returns to the show, or if The Timeless Child story will be retconned entirely. Chris Chibnall said in a recent interview that he doesn't believe Davies will keep any of the world-building or history that he laid out; however, there is no way to know for sure until Davies and the new incarnation of The Doctor begin their run. No matter what happens, for a character that only appeared in three episodes of the series, Tecteun certainly left a mark.