This mode is a reference to the video game Touhou Project. Press C to activate this mode. It cannot be deactivated unless the game is reset or the day ends. Yandere-chan will resemble the popular character Cirno. Her uniform will change to resemble a dress. Her sweater vest will be light blue and her skirt will be light blue and white, resembling the bottom of Cirno's dress. Yandere-chan's hair will become a sparkly blue, and her eyes will turn blue as well. White "ice" wings will grow out of her back, so she will fly everywhere she goes. When idle, she will cross her arms.
During this mode, the player can kill students, teachers, and Senpai. By holding the left CTRL button, ice bullets will shoot out of Yandere-chan's hands, hitting anything in their path. If any student is killed by the bullets, NPCs will treat the killed student as a corpse, so no Heroic or Strict NPCs will attack Yandere-chan. Because she is flying in the air, she will leave no bloody footprints if a student is killed with a weapon.
- Yandere-chan's outfit texture will break if she wears gloves.
- Yandere-chan cannot hold a weapon properly while insane in Cirno Mode. The weapon floats in the air and goes through her body.
- If the player carries a corpse in this mode and then drops it, she will walk normally instead of flying.
- Yandere-chan cannot be pushed by delinquents in this mode if she is too close to them.
- If a delinquent runs and hits a player while they are shooting ice bullets, Yandere-chan will not become comatose, she will not fly anymore, and the delinquent will continue to chase the player without harming her.
- The game's warning referred to this mode, saying that this game contained "murderous ice fairies". This warning was later removed because YandereDev said that it was "cringey".
- This Easter Egg was implemented in the October 10th, 2015 Build. The music for this mode was replaced in the May 1st, 2016 Build.
- Because C must be pressed to enter this mode, the disabled copyright button was changed to D.
- If Senpai is killed in this mode, he will respawn the next day.