“Breeding Diary” – A mysterious notebook that has been secretly passed down from graduate to current student at a certain high school. Only some knew about its existence, and even fewer knew the outline of the Breeding Diary. The main character, Sakuma, is at the mercy of rumors about the “Breeding Diary” but strives to uncover the truth. ――And behind the birth of the “Breeding Diary” that finally arrived, there was a….