Avis is a Mindrunner, a person who has the ability to enter people's minds and implant or remove memories which come in the form of butterflies. Mindrunning is considered illegal, as it is often used for stealing memories (which are then sold on the black market, where other Mindrunners implant them in new minds or simply analyze them for their information) or malicious acts such as giving people amnesia.
Some Mindrunners, such as Avis, offer services where they enter a client's mind and implant or remove memories at their request. Whilst the clients are always completely willing, it would still be illegal if he was caught.
While navigating the world, the mind world of any person can be entered (excluding those who have some sort of defense set up, whether it be an anti-Mindrunner helmet or implant or a mental block). Mind worlds are inhabited by two things: Souls, and Memories (butterflies). Souls are representations of the person's personality and mental state. Vilesouls are hostile souls who are created by negative emotions, while Kindsouls are especially friendly souls created by positive emotions.
To bring a butterfly to or from a mind world, it must be photographed. Butterflies in the real world can be photographed any number of times, but butterflies in mind worlds disappear after a photograph is taken of them. A butterfly photograph can be used while inside a mind world to add the memory to the host's mind, destroying the photo in the process.
If a photo is taken of two or more butterflies simultaneously, when it is used only a single butterfly will be created, with a combination of the traits of all the butterflies in the photo. Photographs cannot initially be used in the real world, although certain items allow the butterflies detailed to be cloned.
Each butterfly has two sets of traits: Physical, and Memory. Physical traits concern the butterfly's physical manifestation in the real world, while Memory traits concern the type of memory it is when released into a mind world.
Breeding occurs automatically between any two butterflies of opposite gender in the same habitat. The result is a butterfly which shares all of the Physical traits of both parents (and, in the case of different values for the same trait, the average of the two), and the Memory traits of one parent, either randomly chosen or determined by the Hereditariness trait.
After a butterfly dies, photographs can still be taken of it. However, dead butterflies are obviously incapable of further breeding.
- Attractiveness: Attractiveness is the likelihood that the butterfly is chosen by any other butterfly during the automatic breeding process.
- Lifespan: Lifespan is the length of the butterfly's life before it dies.
- Hereditariness: The likelihood of the butterfly's Memorial traits being passed down through breeding.
- Lucidity: The clarity of the memory.
- Positivity: The effect the memory has on the host's mental state. High positivity makes them feel more positive emotions, whilst a negative value causes negative emotions.
- Combiner: Allows any two photographs to be combined at any time, creating a new photo that contains the butterflies from both. Can be used to quickly inject new traits into an existing memory in a mind.
- Cloning Machine: Allows any butterfly to be cloned, creating a new butterfly with identical traits. Can only be used from the Lab.
- Photo Reader: Allows a butterfly to be cloned from a photograph, allowing memories taken from a mind world to be manifested in the real world. Can only be used from the Lab.