Well, first you have to ask the other person.
Will: Will you be my parabatai, Jem?
Jem: What, you think I have a death wish?
Will: You’re way closer to the mark there than you think, buddy.
Jem: I don’t know.
Will: If you don’t, I will threaten suicide, and lie in Hyde Park crying while the ducks walk over my prone body.
Jem: Well, all right then.
Jace: Alec Lightwood, will you be my parabatai?
Alec: You are just … so good-looking.
Jace: Yes, that’s what everybody says whenever I talk. So, yes or no?
Alec: I don’t know what you said, but sure. Whatever you want.
After that you have at least six months where you train together, and various officials come and interview you together, and make sure you realize The Magnitude of the Decision You Are Making. When you finally do the ceremony it involves, as Will recalls in Clockwork Prince, two circles of fire on the ground, and one of you stepping to join the other one so it becomes one circle. You say the words of the ceremony, and you use your steles to give each other the parabatai rune. And then you’re done except for there being another round of testing you have to pass before you both turn eighteen. And the angst.
Cassandra Clare= My new favorite person.
So, me and two of my Whovian friends have a head canon about the new Doctor.
Number twelve is very disoriented, doesn’t know how to fly the TARDIS, doesn’t remember people’s names, nor The Girl in the Fireplace.
Take note that the time lords gave him another regeneration, as number eleven was dying.
What if, they didn’t just give him one regeneration, they RESET his regenerations?
So now he has eleven more regenerations. And, he’s still the Doctor, but he’s sort of a new person as well? And that’s why he’s so different from all the others. Why he doesn’t remember things he should remember.
And there is my head canon.