The Piper (Doctor Who/Penny Dreadful crossover)

""Who are you?" "I'm the Piper. And no, not the Pied Piper. Just the Piper."

"People actually call you that? 'The Piper'?" "Some prefer just Piper.""

- Piper and Ethan Chandler Chapter 1

Early life
Raised on Gallifrey, the Piper was given a name that can never be spoken. Upon going to the Academy with her best friends ever, the Doctor, the Master, and the Scholar, she got top marks on nearly everything. However, the Scholar was always a point or so above her. This was the source of much playful picking-on by the Piper.

At some point she was either appointed a TARDIS or she stole one. No one asks, but her friends from home know.

Through the Story
In the beginning of the story, her latest companion, Kayja, was an alien who was furious at the Piper for unknown reasons. She lands the TARDIS, but not where she should've been.

Death
The Piper has only died twice and has 10 Regenerations left.

Post-mortem
Every time she comes back, the Piper is dazed, can't focus, is constantly exhausted until all Regeneration energy is used up. Though practically invincible until this happens, she still does not rush into danger.

Personality and traits
The Piper is constantly guilty of everything in her past. She has a very strong will and can go through years of torture. Due to past reincarnations and her affiliation with the Doctor, she's learned to be cautious.

It is clear she has loved and lost. She choses her companions carefully so they can take it. She has abilities and gives her companions a key necklace that stops their aging, but they aren't immortal nor do they regenerate. Once the companion decides the adventures are over, she drops them off, takes the key back, and moves on.