Dismemberment

Dismemberment was one of the ways to dispose of your rival in Yandere Simulator.

It was the second way to dispose of a rival to be programmed to the game. However, YandereDev removed it because it caused glitches and required revision, so it is currently not implemented in the game.

YandereDev has mentioned via Twitter that it would get implemented eventually in the future again, and that the cello case is there because he was beginning to implement a new feature, but didn't have time to finish it. The cello case has made a small appearence on the rooftop on the August 12th update next to Midori Gurin. At the moment, you can only pick it up and drop it. In the future, the cello case will also have another function aside from dismemberment, but YandereDev has not revealed the extra purpose yet.

Purpose and gameplay
This mechanic has the purpose to carry corpses around school grounds without the risk of getting spotted and/or discovered by other students or teachers.

After killing a student with a sharp weapon (such as a knife) there was an option that would allow Yandere-chan to cut her victim's body into pieces and carry them individually. Dismembering (as well as murdering) the victim lowers the Sanity Meter. After dismembering the victim, the player had to use a cello case to hide the parts of the body and later, throw them in the incinerator. Afterwords, you needed to change into a fresh uniform in order for students to not see you covered in blood.

You may need to join the Light Music club in order to non-suspiciously carry the cello case around.

Trivia

 * When dismemberment is added, it will be implemented in whatever way creates the fewest problems regarding NPC reactions.
 * Dismemberment was showcased on August 1st, 2014.
 * You had to carry each body part one at a time: Head, torso, right leg, left leg, right arm, and left arm.
 * The new cello case was implemented August 12, 2015.
 * YandereDev first called the cello case a guitar case in the video below. He later said on twitter that it was a cello case since cello cases are bigger.