The fifth time Willow met the Doctor was also the last time. It was also the only time she had come to find him.
He was in Cardiff with Martha, saying their goodbyes to Captain Jack, when Jack got a strange look on his face. Following his gaze, the Doctor saw a familiar red head walking through the Plaza, arms feeling the air around her as if it were water. Several hugs, introductions and greetings later, the Doctor was floored speechless.
“I can help you get Rose back,” were the words that stunned him.
“There's a weak point in the Rift, just over there,” she told him, motioning to the water tower. She explained about making a tiny tear between this universe and the one Rose was in, and how she could send him across to find her, then pull them both back before sealing the tear.
The Doctor argued long and hard, then Willow told him in the calmest of voices that she was going to do it anyways, and so he might as well take the opportunity that was presented to him. It wasn't until she cupped his face and looked deeply into his eyes, that he finally gave in. He saw the energy crackling through her eyes, and understood what was happening.
“How long do you have?” he asked her.
“A year, maybe,” she said, and he felt his hearts sink at that. They both new that ever since her Elemental DNA had been awakened, it was only a matter of time before it took over completely. Those few strands of ancient genetic material were all that was needed for her to become part of the energy she controlled.
Opening a path between two different universes, creating a stable bridge that would last several hours and then closing it back up before two worlds destroyed each other was the least of her problems. Willow also had to make sure nothing else went through, in either direction. The energy she would need to absorb and control to stabilize a miniature doorway between universes would be too much for her human body, forcing the Elemental DNA to take over.
By the end of the day she'd be pure, transdimensional energy.
“I'm going to change eventually, and I want to do it on my own terms, rather than wait for it to consume me from the inside slowly,” she countered. She didn't want to spend the next year waiting for her body to burn itself into another form, and he understood that.
“Are you sure?” was his final question, though he already knew the answer.
He asked her how long she could keep the tear open, and she replied, “A couple of hours.”
And so with a tentative mind link as a tracer and the encouragement of both Jack and Martha, the Doctor was gone through the Rift.
After several sweaty hours spent burning off some excess energy with Jack, Willow bolted upright in the TARDIS, her skin burning hotter each second.
“He's got her,” she told Jack, feeling her connection to the Doctor extend itself to Rose. Dressing quickly, they made their way back outside to where the tear between dimensions remained, meeting Martha as she came back from an afternoon of wandering around Cardiff.
Minutes later, the Doctor reappeared next to Willow with a familiar blonde in his arms.
“It's time to close the tear, Doctor,” she told him.
“Thank you, Willow,” he said, echoed by a teary Rose.
As they watched, heat began to rise from her body as she concentrated on closing the hole she'd made between universes.
Soon, flames beginning to lick at her arms and legs, moving to encompass her entire body.
“Thank you, Doctor,” she told him, once the tear was sealed, her eyes blazing golden energy. “You've helped me in more ways that I can ever repay.”
“Take care of him, Rose,” she told the blonde, smiling at the tears that were pouring down her cheeks. “You too, Martha. Keep him in line.”
Finally, she looked at Jack, “I will always remember you, Jack. My Captain.”
Then she let the energy consume her, and with arms outstretched, looking like the phoenix rising from the ashes, she transformed into a wave of golden energy and disappeared.
The first of a new breed of Elementals.