Kyubey

Kyubey is a creature who makes contracts with young girls to turn them into "magical girls" so that they can fight witches. In this process, the girl makes a wish and Kyubey grants it, but in return, the girl's soul is put in a small gem, which is also the source of their magic. If destroyed, the magic will disappear and the girl will die. If it is corrupted with darkness from grief, the gem will turn into a grief seed and the girl will turn into a witch. This is the ultimate fate of all Magical girls. Much like the rest of its race, Kyubey does not possess any human emotion. As seen in a later episode, Kyubey refers to magical girls' bodies as empty shells while explaining why Sayaka "died" when separated from her soul gem.