Kaori Shiraishi holds the position of student council president at Juu Juuzawa's school. Her past is haunted by the belief that she "killed" a boy by rejecting his romantic feelings, driving him to suicide. This boy was Kazuko's brother, whom Kaori abandoned for another man she perceived as offering greater financial security; her rejection directly contributed to his death. Following this event, Kazuko began a campaign of harassment against Kaori, escalating to a physical assault where Kazuko attempted to force Kaori to mutilate herself.

The exposure of her past and the trauma from Kazuko's attack triggered a severe mental breakdown in Kaori. During this unstable period, influenced by the "Happiness Club's" ideology that stealing others' happiness increases one's own, she attempted to murder Juu by pushing him into traffic to metaphysically claim his happiness. The vehicle swerved to avoid Juu but collided with Kaori instead, crushing her against a wall and causing her death. This outcome is framed within the narrative as laser-guided karma.

Kaori Shiraishi is categorized among the story's yandere figures due to her obsessive traits and violent actions stemming from psychological instability.