MetamorphosisThis section was actually added as a response to two different writing prompts at Bad Ass Bitches. The first simply stated that the female character must undergo a metamorphosis of some sort, but left the interpretation up to each site owner. A metamorphosis is defined either as 1) a change of the form or nature of a thing or person into a completely different one, by natural or supernatural means, or 2) the process of transformation from an immature form to an adult form. I think this concept can be applied to Sayaka in both ways. Through various events in the story, Sayaka basically loses her innocence and is forced to grow up. In the beginning of the series, Sayaka is a care free, energetic and reckless middle school girl. She as a rudimentary sense of justice that is very black and white. Things are either right or wrong, good or evil. Sayaka seems to believe that justice prevails over evil as a rule and that good things happen to good people while bad things happen to bad people. After witnessing Mami's horrible death, realizing she's lost her humanity and losing Kyousuke to Hitomi, Sayaka's innocence is stripped away one piece at a time. She realizes that justice doesn't always prevail over evil (Mami's death) and that sometimes bad things happen to good people (people being prayed upon by witches, Mami's fate, realities of life). Sayaka is also forced to toy with the idea that justice isn't always absolute and that it's not human nature to be a defender of justice all the time. Her energy, cheerfulness and confidence are replaced with ugly feelings such as jealousy, hatred, anger, disgust and despair. Sayaka grapples with the fact that life isn't fair and that things don't necessarily work out in the way you want them to, even if you have good intentions.
Sayaka's growth doesn't end in despair, however. Part of maturing from a child to an adult arguably involves overcoming challenges and accepting life's imperfections and inequalities. After being saved by Madoka, Sayaka's regrets, anger, hurt and jealousy all resolve into a peaceful acceptance. She remembers the reason behind her wish to heal Kyousuke's hands and is able to smile (albeit crying) while looking over Kyousuke and Hitomi. She is able to move on and honestly say she no longer has any regrets. Sayaka is able to assist Madoka as part of the Law of Cycles because she accepts that life is unfair, good people get hurt, and struggling with ugly emotions doesn't make you a bad person. She learns life lessons the hard way because of her supernatural circumstances, but she is still able to grow from them and mature emotionally because of it. Sayaka didn't get a chance to actually become an adult. Even so, I think emotionally she was able to grow from an immature middle schooler to a place developmentally more mature.
The Road to Hell is Paved by Good IntentionsAdditionally, Sayaka's belief that the world is precious and deserves to be protected unconditionally gradually evolves to a disdain for the world and the people in it. This metamorphosis is physically represented by the transformation of her soul gem into a grief seed—being a magical girl that transforms into a witch. Ironically, Kyuubey even refers to witches as being the mature form of magical girls! Not only does this represent a metamorphosis of one form to a completely different one physically, but it is also a personality change. Sayaka wanted nothing more than to be a defender of justice when she first found out about magical girls. She was so full of energy and life. One of Sayaka's biggest personality traits was working hard for others, even. Nothing short of a complete metamorphosis could have made Sayaka reach a place so dark that she no longer felt the world was worth protecting. She cursed the world and spread despair as a witch. Not all transformations are good, after all.
Sayaka made a contract with Kyuubey with good intentions. She used her wish for the sake of someone else. She wanted to heal Kyousuke's hand and thus end his suffering and depression. She wanted to see a smile on his face again. In exchange, Sayaka was going to be a defender of justice and protect her city. Yet, through a series of unfortunate experiences, her good intentions ended up transforming into jealousy, guilt, regret and despair. These feelings cause Sayaka to turn into something she abhors and something that suffers for as long as she exists—basically hell. Sayaka's story just goes to show that even someone acting with the best intentions can still cause unforeseen, negative consequences. A good person can become twisted, jaded and unjust via terrible experiences and major stressors. Sayaka never would have imagined becoming a person who could curse the world and hurt her friends. Her experiences as a magical girl, however, challenge her perceptions of her self, the world and others, and she becomes both twisted and jaded. Her negative experiences resulting from her wish caused hope to transform into despair. If Sayaka hadn't made her wish for someone else, perhaps her deterioration wouldn't have happened as quickly, if at all. Making her wish in order to protect the people of the city in Mami's place and for Kyousuke ultimately paved Sayaka's road to destruction.