Witches are evil creatures that provide the primary opposition to the Mahou Shoujo. Witches will affect humans near them through the use of the Witch's Kiss, a mark that can cause accidents or drive a human to murder or suicide. Once a witch is disposed of by a Mahou Shoujo, they will drop a Grief Seed, which the Mahou Shoujo can use to control the darkness in her Soul Gem. Witches are also known to summon familiars to defend themselves or maintain their magical constructs. A familiar can eventually grow into a new witch after it consumes humans.
Witches are born when a Mahou Shoujo’s Soul Gem is tainted and becomes dark. Damaged Soul Gems will cause their hosts to fall into despair and eventually become witches. A Soul Gem's darkness will spread when its host uses magic, and if enough magic is used, the damage will be permanent and a witch will be born. Moreover, the negative feelings from the Mahou Shoujo themselves can act as a catalyst to hasten the Soul Gem tainting process.