The following covers what the general public knows about witches & magical girls. Some of it is wrong.
Witches
- Witches are monsters created from the negative emotion of humans. They try to spawn more of themselves by causing suicides, killing people, and generally spreading despair.
-- Normal humans cannot effectively fight witches. If you see one, run.
- Witches, with only a few exceptions, are too weak to survive in the outside world. They hide within pocket dimensions called "barriers" and target those who wander nearby.
- Witches can gain new abilities by killing magical girls.
- Witches will often adopt a form based on the circumstances behind their creation. For example, a witch born from the negative emotion created by a hospital might take the form of a syringe.
-- Witches are weird.
- Witches specifically target girls with magical potential, as a sort of pre-emptive strike.
Magical Girls
- Magical girls are created by Kyubey, an adorable creature which the Internet has fondly labelled a "bunnycat".
-- Kyubey has multiple bodies and can operate them all independently of one another. It's unclear as to if he's a hive-mind race or just one entity with multiple bodies. Most people assume the latter.
-- The vast majority of humans believe Kyubey to be a spirit created from positive emotion.
--- Many believe that if there's a large enough concentration of positive emotion, Kyubey will gain another body.
-- Kyubey can speak, and be spoken to by MG candidates / magical girls, telepathically.
- Whereas witches are the physical manifestations of despair, magical girls represent hope.
- What marks someone as "qualified" to become a magical girl is unknown.
- If the source of a magical girl's power completely runs out of energy, they will die.
-- It can be recharged, but few people know the specifics. Most people assume Kyubey does it.
-- If the source of their power is destroyed, they will die.
-- Once a person becomes a magical girl, they cannot be turned back into an ordinary human.
- Males cannot become "magical boys", much to the displeasure of many of them.
- In exchange for a lifetime of fighting witches, magical girls get to have a single wish fulfilled. It is not all-powerful and the exact limitations are unknown.
- Magical girls can use magic. Duh.