It was time. The weary old Twelfth Doctor nearing his end stepped forward, pulling the lever of the TARDIS console in front of him. The ship roared to life, its normal wheezing engine signaling the beginning of its journey through time and space. The Doctor turned to the monitor, admiring the display for just a moment.
"Oh, there it is... Silly old universe. The more I save it, the more it needs saving." The Doctor said, pondering this regeneration's life up to this point. "It's a treadmill." To this, the TARDIS responded, an almost frustrated noise coming from it, the Doctor beginning his retort with a sad-sounding sigh "Yes, yes, I know they'll all get it wrong without me." Once again, the TARDIS interrupted with a noise.
The tired Doctor replied to the machine softly, resting his hands on its console. "Well, I suppose one more lifetime... Wouldn't kill anyone." A glance down to his hand... A faint orange glow emanating from it. The sign of the beginning of regeneration. The regeneration he's fought so hard to this point to stop, finally becoming unstoppable. "Well, except me."
The TARDIS hummed as the Doctor took his hands off of it, turning around and talking to the consciousness he could feel coming up to bat next. "Now you wait a moment, Doctor! Let's get it right. I've got a few things to say to you. Basic stuff first." The Doctor began wandering around on the upper floor of the console room, looking down at an imaginary figure, recounting all the things he's done that he regrets.
"Never be cruel, never be cowardly. And never, ever, eat pears! Remember - hate is always foolish... And love, is always wise." The Doctor began his lecture, adding more pep to his step, almost dancing around. "Always try to be nice, and never fail to be kind. Oh, and... And you mustn't tell anyone your name. No one would understand it anyway. Except..." As the Doctor continues, he walks back down near the TARDIS console, and collapses to the ground as his body starts to finally fail.
"Except... Children. Children can hear it. Sometimes - if their hearts are in the right place, and the stars are too. Children can hear your name." The Doctor groans as he starts picking himself up. "But nobody else. Ever." And he stands up, facing his reflection in the TARDIS' centerpiece. "Laugh hard. Run fast. Be kind." One last look... One last reflection on this face. A content smile spreading along it. "Doctor... I let you go."
And with those final words, the regeneration began. The Doctor exploded in a brilliant yet violent burst of orange energy... Warmth. A sudden shift in bodily features, the now baggy clothes draping over a different figure. A ring the twelfth had worn on his index finger slipped off and clattered along the floor as the new figure glanced around, curious, like a newborn child witnessing the world for the first time.
Everything clicked, all of a sudden, as this new Doctor spotted damages to the TARDIS. "I have got to stop regenerating in here... Or get a regeneration room added, or something - Oh." The Doctor reached up to their features, their face was slender, feminine. And so were their fingers. Reaching over and grabbing the monitor, they pulled it over and looked into it as though it were a mirror, yet the unfamiliar sight of a blonde woman greeted them.
The Doctor stood agape as they realized who they'd become. A woman? And still not ginger? They ran their fingers through their hair. "I'm a... Woman? This might take some getting used to." They stopped admiring themselves for a moment and actually looked at the monitor. The TARDIS appeared to be bound for Earth, somewhere around the year 2019, about noon or so. "Brilliant, I love Earth... I think." The Doctor pondered her statement and absentmindedly tapped away at some buttons to set the specific coordinates for Cardiff.
Suddenly, the TARDIS hiccupped. A stutter and a shake, throwing the now lightweight Doctor off-balance in the large shoes she no longer fills, she fell to the ground with a grunt and looked at the TARDIS with shock. "Are you alright? I couldn't have possibly damaged you that much, now could - urp!" The Doctor slams to the ground unwillingly, nausea taking over as residual regeneration energy flies from her mouth. "Oh, no, that's not a good sign..." All at once, she feels the after-effects, collapsing, unconscious.
The TARDIS continues hurtling at maximum speed, its sole pilot and passenger unconscious. The cloister bells ring, but to no avail. The TARDIS crashes out of the time vortex and into a back alley, the blue exterior now covered in burn marks. The TARDIS powers down, almost completely lifeless. Rain begins to pour from the sky outside, cooling off the hot exterior.