Kyouko is a puella magi, a young girl granted a wish in exchange for servitude in fighting monsters called witches. All is not well, however, and the girls have their souls placed in fragile gemstones, appropriately called "Soul Gems"--when inactive, Kyouko's takes the form of a ring, and when active, she wears it as a pendant hanging off the collar of her dress. Puella magi are, as found out later, simply the immature forms of witches, forced to turn into exactly who they fight when their grief and despair become too much, or they overtax their powers, shattering their Soul Gems with darkness. Additionally, if her Soul Gem is shattered, she will die instantly, and if her Soul Gem moves from 100 meters of her, her body will go limp and lifeless. She needs to go through a transformation sequence to go into puella magi mode.

It's not all bad, however; at least Kyouko was granted powers in exchange. She is many times more agile than a normal girl, able to leap hundreds of feet, and send herself flying large distances from momentum. She has a higher pain tolerance than most humans, and she holds a mild regenerative power. Her signature weapon is a spear with multiple chained links, able to stretch for many, many feet. The anomaly with Kyouko is that she can summon this thing while not transformed. She's also able to create small protective barriers, but these shatter if she gets injured badly enough.