Let me tell you the truth about Kyuubei from the words of fellow Magical Girl, Akemi Homura.

There's no source?

ayeraven said:
When Mitakihara is in ashes...you have my permission to die.

Homura: You think a wish on them is worth it. There's a storm coming, Kaname Madoka. You and your friends better batten down the hatches, and when it passes, you'll all think that it was just a freak coincidence, ripping everything apart and leaving little behind.
Madoka: You sound like you've seen this before.
Homura: I've been through a lot.

Homura: You are as precious to me as you are to your own mother, father, and brother. I swore that I would protect you, and I haven't.
...
Kyubey: When the universe is eternal, you have my permission to die.
...
Kyubey: Impossible.
...
Madoka: Fulfill my wish. Then you and the universe have my permission to die, incubator.

Kyubey: I'm in charge.
Madoka: Do you feel in charge?
Kyubey: I've granted you your wish.
Madoka: And this gives you power over me?
Kyubey: What are you?
Madoka: I'm their hope. Here to end the suffering you've all been living on.

Homura: You could’ve lived a normal life, did anything, but you came for all of us.
Madoka: You came for me...
Homura: I guess we're both suckers.
*and then Naked Magic Space Hug*

A hero can be anyone. Even a girl doing something as simple and reassuring as telling you that they will always be your friend.

Actually its amazing!

solisel said:
Homura: You think a wish on them is worth it. There's a storm coming, Kaname Madoka. You and your friends better batten down the hatches, and when it passes, you'll all think that it was just a freak coincidence, ripping everything apart and leaving little behind.
Madoka: You sound like you've seen this before.
Homura: I've been through a lot.

Homura: You are as precious to me as you are to your own mother, father, and brother. I swore that I would protect you, and I haven't.
...
Kyubey: When the universe is eternal, you have my permission to die.
...
Kyubey: Impossible.
...
Madoka: Fulfill my wish. Then you and the universe have my permission to die, incubator.

Kyubey: I'm in charge.
Madoka: Do you feel in charge?
Kyubey: I've granted you your wish.
Madoka: And this gives you power over me?
Kyubey: What are you?
Madoka: I'm their hope. Here to end the suffering you've all been living on.

Homura: You could’ve lived a normal life, did anything, but you came for all of us.
Madoka: You came for me...
Homura: I guess we're both suckers.
*and then Naked Magic Space Hug*

A hero can be anyone. Even a girl doing something as simple and reassuring as telling you that they will always be your friend.

Inconsistent character assignment, off rhythm with the actual line, but it's here.