Homicide

Homicide is a messily but quick way to eliminate someone in Yandere Simulator.

In order to murder, you need a weapon. With a weapon equipped, you can attack a nearby NPC. Your uniform will have several splatters of blood on it, and your sanity will have decreased. The more you murder, the more blood there will be on you, and the more sanity you will lose. Once you've killed four people your sanity will be at its lowest. Those you've murdered will not return to school the next day unless you restart the week or day, except for teachers who respawn.

The protagonist only will be able to kill a teacher with a weapon if she has enough study points for the Physical Education class in order to have enough strength to attack/counterattack teachers, but this has not been implemented yet. Trying to attack a teacher now will result in being expelled. Currently, the only way to kill them without mods is with Cirno Mode. If a teacher witnesses the main character murdering a student, or has realized that she is the murderer, the teacher will chase her down and pin her to the floor once the teacher has caught up. It is not possible to outrun a teacher yet as they have a faster run speed. One way to get away from them is through teleporting, but where to go depends on the build. For some of the first school builds the balcony of the gym might be an option. For the second school builds, the barrier around the main school building will keep foes at bay.

As of the September 1st, 2015 Update, people will scream loudly if they are murdered. Almost everything, if everything involving murder will lower the School Atmosphere, even if any evidence of it is cleaned up. Those in the scream's range will turn around and scream as well. The only way to murder students with the worst School Atmosphere without being caught is to do it in a secluded area, like a bathroom, far away from other NPCs so nothing can be heard nor seen.

In future updates, as sanity drops, killing animations will take longer, and after a student witnesses two murders, they will flee immediately. At low School Atmosphere, students might take out their phones and take a picture of the murderer immediately after they witnessed the murder, which could lead to an instant Game Over.

When the main character kills unnecessary students, she loses events that happen in the storyline (e.g. killing Saki so she cannot have her rooftop conversation with Kokona).

Witnesses
When a student witnesses Yandere-chan murder another student, the witness may react in several different ways depending on their persona. So far, only four personas have been fully implemented into the game: Coward, Teacher's Pet, Strict and Hero.

Coward
If a student with the Coward persona witnesses murder or sees a corpse, they will flee the school and call the police, giving the player a total of 5 minutes to dispose of the corpse, blood, and any other evidence. If Yandere-chan manages to do so, the police will not be able to uncover any evidence that a murder had taken place on school grounds, and Yandere-chan will not be arrested.

Teacher's Pet
If a student with the Teacher's Pet persona witnesses a murder or sees a corpse, they will run to their favorite teacher and inform them of what they have seen. The teacher will request the student to lead her to the corpse. If Yandere-chan has cleaned up the crime scene before the teacher arrives, the teacher will accuse the student of pranking her, and will then return to her classroom. This will leave the witness mentally scarred for the rest of the game. In the future, the witness will try to convince the other NPCs that Yandere-chan committed murder, impacting her reputation negatively. If more than one student with the Teacher's Pet persona witnesses murder, every one of them except the first witness will hide in their classroom instead of informing a teacher.

Hero
If a student with the Hero persona witnesses a murder that is not a murder-suicide, they will try to apprehend the main character by chasing after her. If they catch up and grab her while she has a weapon, this will cause them to enter a “Struggle” minigame, where the player has to press several buttons rapidly in order to fight back and kill them. If she fails to get out of their grasp, they will pin her to the ground and a Game Over will appear. If the main character has no weapon then she will be pinned down immediately once the student catches her.

Evil
This persona has not been implemented yet. If a student with the Evil persona witnesses a murder, they will congratulate the player character on her kill and swear to remain silent about the event.

Fragile
This persona has not been implemented yet. If a student with the Fragile persona witnesses a murder, they will beg for her to not kill them. The protagonist can choose to let them live or die.

Cleaning Up After Murder
The first thing the player should do is dispose of the corpse. Grab the corpse by one of their four limbs and walk to the incinerator which is located to the left of the school gate.

Dump the body and bloody weapon into the incinerator, dispose of the bloody uniform (the clean uniforms are located in the Shower Room), fill the bucket with water from a sink, and mop up the blood (the mop, sink and bucket are currently located to the left of the incinerator, on the first floor in the female bathroom, and on the rooftop in front of Midori Gurin). Stepping into pools of blood will leave bloody footprints that you will also need to clean up. The player can use Yandere Vision to find any blood that may have missed. Dragging a body also creates more pools of blood as it bleeds out. If the mop is too saturated with blood and turns bright red, dip it in the bucket (requires water). The water will get bloody as the mop dips in it. If the water gets too bloody, empty it in the sink and fill it up again.

At this point, the protagonist should activate the incinerator, erasing all of the evidence. As of the August 12th, 2015 Build, she can obtain a new clean uniform in the Shower Room, unlike previous builds, where a new uniform was located next to the incinerator. Once a weapon has been incinerated, they will respawn the next day.

Failure to Clean Up
If Yandere-chan fails to complete all of the tasks necessary to get away with murder, then one of the following things will happen:

Witnessed by a student
Coward Persona: If a student with the Coward persona witnesses the protagonist committing murder, Yandere-chan will be taken into custody by the police, and if there is evidence of her being the murderer, she'll be arrested. If the murder can't be linked to Yandere-chan, she won't be arrested, but she'll have a nightmare that night about losing Senpai.

Teacher's Pet Persona: If a student with the Teacher's Pet persona witnesses murder but all evidence except for the body is gone, the teacher will eventually find the body (so long as they don't bug out) and call the police and remain by the student's corpse, guarding it until the police arrives. The police will not be able to link Yandere-chan to the murder because of a lack of evidence. However, if there is any evidence left with Yandere-chan and a teacher sees her the teacher will realize Yandere-chan killed the student. She will then chase Yandere-chan and eventually pin her down unless avoided, resulting in her being expelled. If the police arrives and there's still things that link Yandere-chan to the murder, she will be arrested.

Not witnessed by a student
If there are no witnesses, a teacher will come across the corpse when the school day has ended while walking through the school to tell any lingering students to leave. If there's no incriminating details and only the corpse on school grounds, Yandere-chan will not be arrested. However, if there is any evidence with it, the police will arrest Yandere-chan. The School Atmosphere will drop by ten points per corpse on the ground.

If pools of blood, bloody weapon(s) or a bloody uniform are left out in the open after the school day ends, a teacher will find and question it, but will not call the police. If Yandere-chan doesn't fix her sanity before school ends then a teacher will see her, but not do anything.

Trivia

 * In the future, it should be possible to murder people with your bare hands under very specific circumstances, but not by default.
 * If the entire student body is murdered in a single day there will be a unique special ending (in the final game).
 * An NPC will not report a murder if they hated the victim or have an Evil persona.
 * Murdered students' parents as well as other students will notice the disappearance of the murdered student, which is one of the reasons why the School Atmosphere drops a little.
 * If a student other than Yandere-chan kills another student (available through any student kidnapped, and only when that student's sanity drops to 0% through and torture), the other students won't notice the murder, they will only notice the corpse.
 * There's an upcoming feature where if a student's dead body is found there will be a flower on their desk later.