Why were Sayaka and Kyoko fighting in the beginning, and what caused them to eventually end up as friends?

Question

Why were Sayaka and Kyoko fighting in the beginning, and what caused them to eventually end up as friends?

(Related: Why exactly does Kyoko attempt to save Sayaka?)

Answer 1

Why were Sayaka and Kyoko fighting in the beginning, and what caused them to eventually end up as friends?

After Sayaka contracts with Kyuubey, there are two magical girls in Mitakihara: Homura and Sayaka. Add Kyouko to this, and that makes three. Three magical girls in one city is far too many, and so Kyouko starts by trying to get rid of Sayaka (either by disabling her or getting her to leave Mitakihara). Sayaka was presumably an easier target than Homura, given that she had only just become a magical girl.

So why did they end up as friends? If you read The Different Story, you'll see that Kyouko was a lot like Sayaka when she first became a magical girl (more than a year prior) - she was all about justice and saving people and stuff like that. But then a lot of things went wrong (foremost among them, her father going mad and killing her mother, her sister, and himself), resulting in the angry, cynical Kyouko we see in the show.

I guess she sees Sayaka as being a lot like herself, and wants to keep her from suffering the same things she did. (Kyouko says something to this effect in episode 9.)