Kasami Yume

Kasami Yume is student number 4 out of 15 in the A Planned Game (APG) roster. She is the Ultimate ???, although later in the story it is found out that she is the Ultimate Manipulator. She is a very naive girl, with the iconic phrase "I do not understand!" when expressing her inability to comprehend something. Out of all the students, Kasami suffers from amnesia the most, being unable to recall any memories. She is similar to how a newborn baby who already knows their alphabet may act; she does not have experiences to learn from on how to act in situations, and does most things on impulse (for example, when she jumps in a pool and does not swim out: she can swim but doesn't know she is supposed to swim). Many of the characters think of her as a child, but during trials become suspicious of her cluelessness.

Backstory
Not much is known about her backstory from when she was younger, but it is known that Kasami helped manipulate the memories of the students for A Planned Game. As told by Monoshark, Kasami had believed she was doing a good thing, but her actions ultimately helped the killing game, until she herself was placed in the game with her memories removed.

CD: Manipulator's Lab
she walks to a cabinet next to a large machine with a bed and a hollow cylinder where the head would go, similar to an mri scan

she opens the cabinet and inspects its contents, appearing to ponder for a long moment

she then proceeds to remove what appears to be medicine bottles that are different sizes and shapes, and places them on a nearby counter

to any person passing by, the bottles would appear labeled with long, unfamiliar chemical names.

''she sets one bottle with liquid aside, and places the rest back in the cabinet. she methodically makes sure all of the bottles are organized, slowly placing them back one by one, before closing the cabinet and wiping dust off of the glass cabinet door''

she holds up the bottle, letting light pass through the reddish bottle, which creates orange rays of light on the counter

unlike all of the other bottles, the label of this bottle is not some foreign-sounding chemical compound, but instead says "Kasami's Happy Potion"

the label looks as if a little kid wrote it, with the name being in crayon and in messy handwriting

she searches the drawers in the counter for something, before taking out a white measuring spoon

carefully, she uncaps the bottle and steadily pours it into the spoon, making sure not to spill a single drop

''she sets the bottle back on the counter, her reflection in the cabinet glass door catching her eye. spoon full of brown liquid still in hand, she stares at her reflection, hesitating''

''kasami recognizes the reflection in the glass, yet she can not trust it. every face is the same to her. face after face after face, who's to say the faces are real? even if the faces are real, what's the point of believing the faces will stay? how many of the faces are made up, fabricated from a machine? how many are human, and how many are just visions made up by her own mind? how many are really part of her memories?''

memories...

she glanced at the liquid in the spoon, noting the contrast between the foggy brown and immaculate white

''kasami was not afraid of change, or at least thats what she told herself. people change every day, every second of their lives. they can learn and feel and be different than the person they were yesterday. but kasami knew how easily that could be taken away.''

if a person remembers, then they will believe.

kasami raised the spoon to her lips

she liked it better when she couldn't remember.

the chemical smell flooded her nose, and she felt as if the odor was spreading from her nose, to her lungs, to her brain

she liked it better when she couldn't believe.

she opened her mouth, letting the cold liquid flow down her tongue, and swallowed