Sanity

Sanity is a key element in Yandere Simulator. If Yandere-chan performs an unethical action (such as murder, drowning someone, etc.), then her sanity will decrease. In order for Yandere-chan to be completely insane, she will have to commit murder several times.

When Yandere-chan is visibly insane, Yandere-chan's head and arms will be twitching, and her eyes will be open wide with the pupils constricted. If she commits any murders while visibly insane, her murders will get more sloppy and careless. The music and atmosphere will become slow and slurred, in a far more threatening tone than the usual chords.

If Senpai or a teacher sees Yandere-chan being visibly insane, then it will result in a game over (Senpai giving the 'Heartbroken' ending and teacher giving the 'Expelled' ending).

Meanwhile, If a student sees Yandere-chan in this state, then her reputation will only be damaged. You can apologize to those that saw you to get half of your reputation points back.

YandereDev has stated that Sanity will have harsher consequences and Sanity must be considered in your strategies. There will also be Sanity Determined kill animations. The killing animations will be determined by your current level of Sanity. When your Sanity is high, your kills will be efficient, quick, and silent. When your Sanity is low, your kills will be sloppy, messy, and noisy. When you have lost all Sanity, your kills will be long, brutal, and sadistic.

Cardiograph Monitor
The cardiograph monitor displays Yandere-chan's current heart rate, which reflects her sanity. It is located at the bottom-right of your HUD.

When Yandere-chan has high sanity, the cardiograph monitor will be pink, with the spikes appearing every second or so - a normal, calm heart rate.

When Yandere-chan is fully insane, the cardiograph monitor will be a bright red, with the spikes appearing in quick succession, showing that her heart rate is erratic.

Restoring Your Sanity
In order to restore your Sanity to normal, you can:
 * Laugh hysterically. To do this, tap the Ctrl (PC) or RB (controller) button repeatedly.
 * View pictures of Senpai. To do this, you'll have to take pictures of Senpai using your phone. Then press Enter (PC) or Start (controller) button and navigate to the photo gallery. Select the photo(s) you have taken and 'use' it by pressing the R (PC) button.
 * Stand near Senpai (but don't get noticed for too long, or it will result in a game over).
 * If you laugh in a psychotic way when other students are near, your reputation will drop as of the September 1st Update.

Trivia

 * Yandere-chan's insane laugh is 18 months old.
 * YandereDev has stated that a more accurate measurement would be Composure rather than Insanity, as Yandere-chan is insane 100% of the time. However, she hides it except for when murderous deeds cause her true nature to show.
 * When insane, there are two other pieces of music which resemble the original "Wellness" song which plays throughout the game when fully sane. When nearing full insanity, the music will become distorted in pitch, which can be heard here. When fully insane, the music becomes extremely distorted where you can hear; the pitch in parts of the song heavily decrease, pianos play in the background, and out-of-tune notes. The fully insane song can be heard here.
 * In the animation of third degree laughter, you can see the animation of Yandere-chan's pupils dilating to return back to usual.
 * You will lose more reputation points if you're insane when School Atmosphere is low.
 * In the very old pre-debug builds, instead of a cardiograph, there was a grey meter of a human. After every Yandere action, the meter became more red, showing how much Sanity you have lost. There was also a face cam of Yandere-chan's eyes. After every Yandere Action, her eyes became more dilated and her smile bigger . These two HUD functions were later removed.