A stun gun is a non-lethal weapon designed to incapacitate a person using an electric shock.
Kaori Saeki zaps Academy professor Hiroko Takashiro with a stun gun while she is distracted by student Taki Minase in the art club. She is then brought to Saeki's apartment to be water tortured by the evil Reika Kitami's command.
In the games
In the first game, it is Hiroko Takashiro who owns a stun gun. She first uses one to defend the player Taki Minase and his friend Kurumi Imari from school bully Inoue and his goons. The boys, who attack Minase and abuse Imari in the gymnasium store room, are quite intimidated by the device. Takashiro zaps them several times after coming to her students' rescue.
Used against Kitami's followers
In another storyline, Takashiro hands Minase a stun gun with increased voltage when they try to put an end to Kaori Saeki's witchcraft club in Saeki's apartment. She also gives him a leather glove for protection, as the overpowered weapon might hurt himself. The pair enter the apartment and engage Saeki and her friends Jun and Maki. Takashiro is eventually defeated by the evil witch Reika Kitami and tells Minase to flee. He makes a run for the door and zaps Saeki with the stun gun when she attempts to block him, leaving the girl unconscious and twitching on the floor.
In one storyline, Minase is knocked out by Imari before he can escape after the girl has been brainwashed by Kitami and joins the group. Saeki, still angry about being zapped herself, vengefully electrocutes Minase's unprotected body with the taser, numbing his arms and legs as a strong electric current flows through him.
Minase successfully escapes in another storyline, and he uses the stun gun to again attack Saeki in the art club where Takashiro is being gang raped by several students. The girl deflects the attack, however, forcing Minase to drop the weapon on the floor. As payback, she later shocks him after Minase is forced to have sex with Takashiro.
One of the good endings in the game has Minase and Takashiro finding a man and a woman unconscious near the school gate when they attempt to stop Kitami's ritual in the basement. They were presumably attacked by Takashiro in advance to steal their black robes for a disguise.