Corruption

"Corruption" is a term used in Magical Girl Noir Quest, standing for several different mechanics. In general, it means decay, with fatal consequences if left unattended. The forms are often linked to each other somehow.

Grief

'Grief' is slang for the black, thick-looking matter that accumulates in a Soul Gem over time, or upon using Magic. If there would be enough to fill up the gem, it instead becomes a Grief Seed, and the Magical Girl becomes a Witch.

A lot of Grief in the Soul Gem adversely affects one's mind, clouds their thoughts, and so it often happens that a Magical Girl witches out from only a mostly blackened gem, with rest of the Grief generating rapidly when she loses her focus. Most Magical Girls therefore don't take risk, keep a reserve, and like to cleanse their Soul Gem sooner then they might necessarily need to.

Soul Gem Corruption

Corruption of a Soul Gem and a Magical Girl's own mind is more or less the same thing. It causes the Soul Gem to accumulate Grief faster. It can be caused by the person becoming nihilistic after a negative event in their lives, shutting themselves in, and so on. Exposure to the Akashic Realm also corrupts the visitor's Soul Gem. Such a condition is extremely dangerous to their surroundings and themselves, and every Magical Girl society has a policy to handle such cases. Applying a Grief Seed usually doesn't help a heavily corrupted Soul Gem, as it will simply generate critical amount of grief in a short span of time. Psychological counseling might be necessary instead.

Golden Weapon Corruption

The Golden Weapons, pieces of Blessed Lady's own soul, are known for corrupting their users. This corruption is not necessarily fatal, and consists more of the weapon changing the user to suit its needs. The specific way the user will be turned differs wildly, but can be guessed from the weapon's number, and corresponding Major Arcana. Most of the users will turn murderous, though, since the weapon also wants to be used.

Witch Flesh Corruption

Becoming a Witch, becoming a Maerorus, manifesting Witch-like properties, or eating Witch flesh, is often associated with corruption.

It has not been proven that eating Witch flesh affects one's sanity, but it is true that most Magical Girls who eat it are lunatics.

It's likely that Pinky is corrupted mostly in this sense.