Corruption

The Corruption is a major concept within the universe of Highschool DxD: Blazing Dusk & Midnight Dawn. It was created after the defeat of Kaira, the Lady of Chaos, by a previous wielder of the power of Azrael, the Lord of Balance.

Summary
When Kaira was defeated, her spirit released an evil force (despite evil being subjective) later dubbed the Corruption due to its effect on its victims.

As the name implies, the Corruption corrupts an individual's heart, taking the undesirable aspects of their personality (again, generally subjective) and increasing their prominence exponentially. It is especially attracted to people with dark or twisted desires. The victim becomes more and more distorted as time goes on, and their view (or rather, cognition) of the world becomes warped. They will begin to see the world in different ways depending on what traits were corrupted. For example, a corrupted politician who became overly arrogant could see the place where they work (such as the American White House, Supreme Court, or whatever building the British Parliament works in) as their own castle to rule, and everyone else is their servant or a peasant to be looked down upon. If the Corruption is left alone and gets too powerful, the victim becomes a grotesque monster with varying degrees of resemblance to the victim as they originally looked, and generally of very large size.

More often than not, the Corruption spreads to the people around the original victim, but in a different manner. Instead of highlighting their worst qualities (I'd like to point out how subjective the world is), the Corruption makes them not notice the original victim's corruption, and they begin to turn a blind eye to their distasteful activities and tendencies. They might even defend the corrupt individual.

Corruption, despite its tendency to latch on to nearby people like a fast-breeding parasite of Chaos and evil, can be dispelled. This is done through an ability dubbed "Heart-to-Heart." The ability can only be used by people who are or were connected to a Primordial Lord (Kaira, Azrael, or Satanael [lord of Order]) or people who were at one point corrupted.

Dispelling Corruption
Corruption can only be dispelled by people who are or were connected to a Primordial Lord or people who were at one point corrupted, as stated above. This is done through an ability called "Heart-to-Heart," named by the Vanguard leader Michael Eon.

The user must first defeat the corrupted individual in battle without killing them, then place their hand over the individual's heart. Both the corrupted individual and the user will be rendered unconscious in reality, then appear in a place known as the corrupted individual's Mindscape. The Mindscape looks different for everyone. It can be a real place, the corrputed person's view/cognition of somewhere, an empty void, or anything else.

The user and corrupt person's souls will be standing or sitting in the Mindscape. The user will try to talk to the corrupted person, convincing it to let go of its twisted desires, sometimes (though not often) ending in a battle between the souls in which the user's goal is to defeat the corrupted soul without killing them, and finally convince the soul to let go of its corruption and become something greater. Neither soul has the capability to lie during a Heart-to-Heart.

If the Heart-to-Heart is successful, the user will reawaken back in reality, and the formerly corrupted individual will still be unconscious. When the victim reawakens, they will be free of their corruption and eventually revert to their original self, as will the others who were corrupted by the initial victim. The victim often enters a temporary state of depression before they begin looking for a way- any way- to atone for their actions. After this, they will either atone for what they did or be convinced that it isn't necessary by someone, usually the user of the Heart-to-Heart. Only then do they go back to normal.

If the Heart-to-Heart fails (by the user's soul being killed in the Mindscape), they will awaken in reality as an emotionless husk, a sorry excuse for the person they once were. Slowly, the user will start to become more and more ill, until one day, they seemingly return totally to normal, until their brain shuts down, then liquefies and starts leaking out of their nose, ears, mouth, and eye sockets as a strange, red and black fluid that's poisonous to the touch and their body slowly dissolves into millions of tiny venomous scarab beetles over the course of a month (if direct contact is made with one of these beetles, you suffer the same fate as the unsuccessful user. The same thing happens if you make direct contact with the liquid). The corrupted individual becomes even more corrupted.

Detecting Corruption
Corruption will make itself known rather early on, but the signs are only able to be read by someone who can perform a Heart-to-Heart. They will know not because of the victim's twisted personality (well, yes they will, but there's another way in case the Corruption is very subtle), but because it will call out to them. They will hear a distorted version of the victim's voice challenging them to defeat it, then hear the victim's real voice cry for help.

Known Victims of Corruption

 * Raynare
 * Riser Phenex (Cured)
 * Ophis