When Yandere-chan kills a person with any weapon, her uniform and weapon will be splattered with blood. Her sanity will decrease with each kill, although wearing the Tiny Thong Panties, belonging to the Occult Club, or increasing Yandere-chan's Numbness level lowers the amount lost. To avoid getting arrested, the player must at least dispose of the uniform and the weapon using the incinerator. In future builds, different weapons may result in different amounts of blood, but this will be determined in the balance phase. One way to balance the weapons would be to make non-suspicious weapons less lethal with longer killing animations.
Currently, there are fifteen weapons the player can use. The only available weapons that can currently be seen on the Challenges Menu are the knife, boxcutter, scissors, screwdriver, syringe, and katana.
Some weapons are considered non-suspicious and will not result in a reputation penalty if Yandere-chan is seen carrying them. If Yandere-chan is a member of a particular club, suspicious weapons associated with that club (such as the shovel as a member of the Gardening Club) will become non-suspicious.
Some weapons can be concealed, while others cannot. The player can check if a weapon is concealable by pressing 1 (PC). As of the February 15th, 2016 Build, the player cannot use a non-concealable weapon when fighting a Heroic student, because the weapon is too unwieldy to use in close quarters and will result in automatically losing the struggle. Any non-concealable weapon can be hidden inside a cello case or a trash can.
As of the December 1st, 2015 Build, the game will track whose blood and whose fingerprints are on each weapon. If the player does not dispose of a bloody weapon, a teacher will find it and call the police. The police will try to trace the weapon back to Yandere-chan. If the player wears gloves, the police will not find Yandere-chan's fingerprints on the weapon. As a result of this, the player is able to frame other students by using weapons they have touched to commit murder. This method can be used after Kokona Haruka uses the knife in the Cooking Club. Since Kokona's fingerprints are the only ones on the knife, she will be arrested for the murder.
In earlier builds, the player automatically dropped all weapons when the day ended. This was troublesome, as a player who forgot to dispose of a weapon would leave it on the ground when they left school. A teacher would then find it and call the police, and the police could immediately trace the weapon to the player. As of the January 2nd, 2015 Build, the player will instead take the weapon home and dispose of it. If the police arrive at school, however, they will search the students and find the bloody weapon on Yandere-chan's body, so she will still be arrested.
- Main Article: Reputation
If students see Yandere-chan carrying a dangerous weapon, they will see her as suspicious, thus damaging her reputation by ten points (fifteen points if School Atmosphere is medium, and twenty points if School Atmosphere is low). Apologizing to a student will give the player back some of the reputation lost. If a friend or a student that is being seduced by Yandere-chan sees her with a weapon, her reputation will be affected by eight points. If the player is in the Occult Club, it will take longer for students to notice the player carrying a dangerous weapon.
If Senpai sees Yandere-chan with a dangerous weapon, he'll become terrified of her, resulting in a Heartbroken ending. If a teacher sees Yandere-chan with a dangerous weapon, she will be expelled. If a teacher sees her holding a dangerous weapon after a student has been murdered, she will assume Yandere-chan killed the student and pin her down, apprehending her. In the future, being seen with a dangerous weapon by a teacher will cause Yandere-chan to get sent to the Counselor's Office.
The scissors, box cutter, and screwdriver are classified as non-suspicious weapons. The player will not be considered "Visibly Armed" when carrying these weapons. In the final game, the only weapons available will be ones found in a school environment, unless the player asks Info-chan to leave a weapon at the back of the school.
If Yandere-chan holds a suspicious or bloody weapon near the delinquents, they will assume a menacing stance, ready to fight. They will lower their guard after she puts it away, and taunt her. If the player holds their weapon near the delinquents for too long, they will render Yandere-chan comatose with a blow to the head. In the future, if Yandere-chan beats a delinquent, she will be able to take their weapon.
- Main Article: Sanity
- Stealth kill: Performed from behind, with victim unaware. Quick, quiet and clean.
Low sanity kill animations will last longer than high sanity ones.
- High sanity kill: Efficient, but not as fast as a stealth kill. Produces some extra noise and blood. Will take two seconds.
- Medium sanity kill: The victim struggles a little bit. The kill is sloppy and messy, thus taking more time. Will take four seconds.
- Low sanity kill: Very prolonged killing animation that is unnecessarily brutal and sadistic. Victim screams and struggles. The player has the option to make Yandere-chan continue to stab her victim indefinitely by mashing the "attack" button, causing a segment of the animation to loop until the player stops mashing. Will take six seconds.
More animations could show additional kill techniques that vary depending on weapon type and current sanity level. Ideally, every weapon will eventually have a unique animation set. If this cannot happen, a less ideal scenario would be that each weapon type (short, stabbing, long, and bludgeoning) has its own animation set. At worst, all weapons will have the same animation.
- Main Article: Axe
Found outside the shed. Seen as suspicious and cannot be concealed. The player cannot fight back with it.
- Main Article: Baseball Bat
- Main Article: Box Cutter
Found in the Art Club. Seen as non-suspicious and can be concealed.
- Main Article: Circular Saw
Found inside the shed. Can also be used for dismemberment. Seen as suspicious but cannot be concealed. The player cannot fight back with it.
- Main Article: Dumbbell
- Main Article: Energy Sword
This weapon is only found when Cyborg Mode is activated. Seen as suspicious but cannot be concealed. The player cannot fight back with it. It will spawn in front of the school gates. When used, it will dismember anyone in the player's way.
- Main Article: Fire Extinguishers
They are found on all floors near the bathrooms, but they cannot be interacted with yet. They will be a bludgeoning weapon in the future.
- Main Article: Katana
Found inside a case in the headmaster's office. Seen as suspicious and non-concealable. The player cannot fight back with it.
- Main Article: Knife
Magical Girl Wand
- Main Article: Magical Girl Wand
Found inside the Drama Club. Seen as suspicious and non-concealable. The player cannot fight back with it.
- Main Article: Ritual Knife
- Main Article: Scissors
Found in the sewing room. Seen as non-suspicious and can be concealed.
- Main Article: Screwdriver
- Main Article: Shovel
Found outside the shed. Seen as suspicious and cannot be concealed. Can also be used to dig and fill up holes in the Gardening Club's garden to bury dead bodies. The player cannot fight back with it.
- Main Article: Syringe
Possibly Planned Weapons
Weapons that might be added in future builds:
- Butcher knife
- Gardening sickle
- Painting knife
- Soda cans - Yandere-chan can get them from a vending machine. In the future, she may be able to put them into a sack and hit students with it, but animations are needed.
- Rena's axe (animations are needed)
- Gardening shears
Blunt weapons are planned and some models are already prepared, but there are no animations for them yet.  YandereDev does not want to add guns to the game, so it is unlikely that any of the thirty planned weapons will include that. There will be different types of weapons, like two-handed, swinging, stabbing, and strangling weapons.
|“||What do you want?! Don't hurt me! Stay away!||”|
— A student seeing a fully insane Yandere-chan bloody and carrying a weapon.
— Delinquents after seeing Yandere-chan hold a weapon.
|“||Don't even think about it!/Run home to mommy before you get hurt./I'm gonna crack your skull open!/You wanna fight?/You must have a death wish./Don't you know I eat girls like you for breakfast?/Try it, I dare you!||”|
— Delinquents while watching Yandere-chan hold a weapon.
|“||What are you doing?! Put that down immediately! You'll be expelled for this!||”|
— A teacher after catching Yandere-chan holding a weapon.
|“||Just what do you think you're doing?||”|
— A teacher resisting Yandere-chan's attack with a weapon before pinning her to the ground.
|“||Why do you have a weapon? What are you going to do with that thing?! Stay back!||”|
— Senpai after seeing Yandere-chan visibly armed.
|“||Yeah, that's what I thought. Coward./All talk and no action, huh./Hahahaha... I knew you didn't have the guts.||”|
— Delinquents after seeing Yandere-chan put away a weapon.
- It is theoretically possible for a pencil to become a weapon, but YandereDev does not find it cool enough. He wants all weapons to be cool.
- If a small town is implemented, more weapons will be available.
- YandereDev has stated in an interview that the katana might be something that the headmaster confiscated and just never got rid of.
- As of the November 15th, 2016 Build, the katana is located in the Headmaster's office.
- Ranged weapons will most likely not be in the game.
- Formerly, there were only three regular animations with a murder weapon: a sideways stab to the neck for the knife, scissors, box cutter, screwdriver, syringe, and ritual knife, a slam to the head for the katana, baseball bat, shovel, dumbbell, and a unique animation for the circular saw. There is also a stab in the head whenever Yandere-chan wins a fight against a Heroic student and another when brainwashed, kidnapped victims finish a murder-suicide. All of the weapon animations have been replaced with the sanity-based attacks, except during fights against a Heroic student.
- The animation used for the larger weapon, high sanity attack animations, (except the circular saw) is also used for when delinquents attack Yandere-chan.
- Yandere-chan intends to kill when the player presses the "attack" button. There is no chance of knocking the victim unconscious.
- There is a possibility that a sniper mini-game will be added purely for fun.
- It is very important to YandereDev that there's a cheat code or Easter Egg which unlocks a giant sci-fi energy scythe.
- In the future, it is possible that if students see a certain weapon lying around they will give it to a teacher.
- YandereDev does not have the animations nor the models for choking someone with a rope or a chain yet. 
- In the future, Yandere-chan may be able to wash the blood off of a weapon in a sink; however, she may also be required to use bleach to wash the weapon properly.