Eiji Urashima is just an ordinary university student like everyone else. His college career consists of boozing with his friends and trying to get a girlfriend. On October 23rd, he returns home after a pleasant night of drinking and goes to bed. To his surprise, when Eiji wakes up, a gorgeous girl from his university, Kyouka Yukimura, is lying beside him—claiming to be his girlfriend.

Having no recollection of the event, Eiji goes along with the flow until he's faced with more nonsensical events that took place in the last few days. Walking alongside his friend, Kashiwagi, he cannot help but ask the most intuitive question in his mind: isn't today the 24th? "Eiji, what are you saying? Today's the 27th."

Three days have passed, yet Eiji cannot recall a thing. The situation takes a dire turn when a magazine writer exposes Eiji's deepest secret in front of Kyouka: he is the son of a serial killer. As his life is thrown into a spiral of disarray, he embarks on a journey to resolve the mess of the last three days and get Kyouka to accept his past.