The TARDIS adored her Thief. Above any other living thing that had ever stepped through her doors, he was her favorite. With, perhaps, one exception.
From the moment her Wolf stepped through her doors, the TARDIS had known this young girl was special, that she was meant for so much more than her human mind could ever have imagined. The TARDIS immediately recognized her significance, that this simple human would one day be so determined to save the Doctor, she would rip open the TARDIS’s heart and absorb the Time Vortex itself. They would become the Bad Wolf, having only one purpose and thought in mind—to save their Doctor.
The TARDIS had watched with trepidation as the Time War slowly tore her Thief apart at the seams. The war had caused him to become someone else, someone who did things that went against all he stood for, the very essence of who he was, changing him into the War Doctor. She had watched with great sorrow as her Thief was faced with an impossible choice; being forced to declare “No More” to his own people, the Time Lords of Gallifrey, and one of his greatest enemies of all time, the Daleks of Skaro, in order to save the rest of the universe.
She had tried to protect her Thief and help him as best she could after the Moment. Yet, with so much loss weighing on him—the destruction and loss of his people, his planet, his family, and even a part of himself—and the mountain of guilt from so much blood on his hands and conscience, the TARDIS felt particularly helpless. She could only watch as the Doctor, lonelier than he had ever been in his lives, had turned bitter, cold and angry.
His loneliness was what made the TARDIS realize that the Doctor desperately needed someone. He needed someone who could help her Thief to find himself again and remind him of who he used to be. One who could challenge, yet encourage him; show him that the universe still had some good in it and that it still needed him, a Doctor to make it better. Most importantly, she recognized that he needed someone to hold him back when he got too close to the edge.
Constantly trying to find a way to help her Thief, the TARDIS searched through time to find someone who could help bring the Doctor some healing and peace, to help put his shattered hearts back together again.
One night the TARDIS alerted her Thief to a disturbance, knowing it would peak the Doctor’s curiosity and natural desire for adventure. She highlighted the fact that there was a life form in the basement of a building in which the Nestene Consciousness was attempting to begin its infiltration of the Earth. They both knew that this was a death sentence to whoever was in the building. The Doctor had not hesitated to race to the basement, desperate to atone in whatever way he could for his actions in the war. Therefore, he did not hear the smug and distinctly happy tone of the TARDIS, and was unaware that he was racing to save the person who would change his life forever.
It wasn’t long before Rose Tyler had permanently woven herself into the hearts of the Doctor—the hearts that she had slowly helped to mend and heal.
The TARDIS was happy because her Thief now had what he needed most: a hand to hold.