The 13th Doctor stood alone on a beach on the planet Barcelona. Her body radiated with yellow energy. She closed her eyes, took a deep breath of sea air, and whispered a near-silent farewell to the universe that she barely began to explore. As the energy surged through her, she opened her eyes, outstretched her arms, and smiled for one final moment in time.
As she surrendered to the inevitable tide of regeneration, her form illuminated the planet with a brilliance that rivaled the stars.
But unbeknownst to her, in this vulnerable threshold between selves, the Solitract reached out across the dimensions, its essence invisible, its touch as gentle as a whisper of thought.
"Oh brilliant," she exclaimed in admiration of the yellow sunset over the greenest ocean in this corner of the galaxy. "That's the only sad thing, isn't it? I want to know what happens next. But I can't. That's not my area anymore. Right then, Doctor Whomever-I'm-about-to-be... Tag, you're it."
In that instant, where time seemed to stretch into infinity, the Solitract wove its presence into the tapestry of her transformation. The Doctor, caught in the rapture of her own rebirth, was unaware as the Solitract tenderly ensnared her being, pulling her into its universe just as the burst of regeneration reached its peak.
And then the Doctor let go for the last time and allowed the energy to flow and overtake her form. The burst of light shined across the entire planet Barcelona and a new Doctor emerged as the light faded. The Doctor looked down at their hands, marveling at the sensations of being reborn on a new scale of bodily proportions.
It was then that the Solitract's universe revealed itself, a reality constructed from the fabric of her own memories and desires. The beach, the sunset, Barcelona itself — all were reflections of the Doctor's own mind, a mirage spun from the Solitract's longing for companionship.
Who was she this time?
Perhaps an even younger woman? No, these hands are somewhat old, nearly wrinkled, but yet familiar.
Perhaps a wise warrior like the lovely lady from Gloucester?
Or a slow-speaking sage?
A cautious coward?
Beautiful?
Sexy?
Suddenly, it was like the pin dropped with that last thought. The Doctor licked their teeth and lips to confirm their suspicions. Their eyes widened with shock realization.
"I know these teeth," the Doctor exclaimed. "What?! What?! WHAT!"