The narrative begins with the protagonist experiencing a recurring, unsettling dream of absolute darkness, a dream he initially dismisses as meaningless. On April 1st, he wakes up in his familiar living room, noting his usual routine and attire. However, turning on the television reveals a horrifying reality: the country is in chaos, with widespread riots and people exhibiting abnormal, violent behavior. The news reports describe an unknown contagion causing people to attack others, with infected individuals displaying glowing red eyes and bleeding from their mouths. Experts are baffled, speculating about a possible epidemic or even comparing it to a zombie outbreak. The protagonist, surprisingly unfazed, meticulously records details from the news and his own observations, including his clothing and a cryptic phrase he uttered. He notes the time, realizing his monthly premonition is about to occur.
The story then shifts to a different morning, where the protagonist, Jin, wakes up with five minutes to spare before his usual 6:30 AM deadline. He performs his morning routine, including writing down the details of a vivid, terrifying dream he had. This dream, unlike his usual dark ones, depicted the same chaotic scenes he witnessed on April 1st. He then proceeds with his established routine of checking stock prices, FX, and Bitcoin, followed by high-payout gambling information, and finally, news sites and social media. This meticulous preparation is a habit formed from his unique ability: a monthly premonition that occurs for one hour, one month in advance. He has learned to record these dreams in detail to ensure their accuracy, as deviations can reduce their predictive power.
Jin's older sister, Yae, a NEET who lives with him, joins him for breakfast. Their interaction reveals a close but somewhat dysfunctional sibling relationship, with Jin handling most household responsibilities and finances while Yae indulges in games and the internet. Yae, despite her age, maintains a childish and eccentric persona. Jin confides in Yae about his terrifying dream, which she takes seriously, recognizing it as his "miracle once a month" ability. They discuss the implications of his premonition, realizing that warning others would be futile as they would likely be dismissed as crazy. They decide to focus on their own survival, planning to fortify their home and gather supplies. Jin's premonition ability is described as flawed: it only occurs once a month, for a single hour, predicting events exactly one month in the future, and requires precise recall to be effective. Yae recalls Jin's childhood premonitions, which were initially dismissed as nightmares until they accurately predicted a near-fatal accident.
The narrative then jumps forward to a period closer to the predicted event. Jin and Yae are actively preparing for the impending crisis. Jin has purchased a significant amount of supplies and is planning to reinforce their home. He contacts a DIY YouTuber named Diya, known for her elaborate home modification videos, offering her a substantial sum of money to transform their house into a fortress. Diya, initially skeptical, accepts the offer, seeing it as a massive opportunity for her channel. Jin fabricates a story about Yae's paranoia regarding security to justify the extreme measures. Meanwhile, Diya's uncle, a private detective, begins investigating Jin and Yae, prompted by Diya's suspicions about Jin's wealth and unusual request. The detective uncovers a tragic past for the siblings: their parents died in a car accident caused by a politician's driver, and they were subsequently subjected to intense media scrutiny and online harassment, leading to Yae's reclusiveness. The detective also notes the unusual circumstances surrounding their parents' wealth and the siblings' current financial situation, finding Jin's request for a fortified home suspicious.
The story progresses with Diya arriving at Jin and Yae's secluded property, a large RC (reinforced concrete) house surrounded by high walls, located by a lake. Diya is impressed by the property's potential for her DIY fortress project. Jin explains the need for fortification, while Diya, eager for content, proposes the concept of "Real Base Building for Zombie Attacks." They discuss the installation of solar panels and other defenses. The detective, meanwhile, continues his investigation, discovering the siblings' parents were victims of a fatal car accident and that their wealth likely stems from insurance and compensation. He also uncovers a suspicious fire that killed their paternal grandparents and relatives shortly before the parents' accident, and the subsequent media frenzy and online harassment directed at Yae. The detective finds Jin's request for a fortified home highly suspicious, especially given the siblings' apparent lack of income and the urgency of the request. He suspects Jin might be involved in illicit activities.
The siblings continue their preparations. Jin decides to clear out their parents' bedroom to store supplies, a decision that deeply upsets Yae due to the sentimental value of the items. Jin persuades her by emphasizing the necessity of survival and the potential to preserve some memories through frozen food. They discover their father had a hidden collection of books, including practical guides for survival, fishing, magic, and gardening, suggesting a foresight or interest in such matters. Diya and her associate, a skilled electrician named Iwao, arrive to begin the fortification work. Jin reveals the extent of his property, which surprises Diya and Iwao. He also shares a fabricated story about the land being haunted, further enhancing the "fortress" narrative for Diya's videos. Iwao confirms the feasibility of installing solar panels on the roof. The detective, through his investigation, uncovers more about the siblings' past, including the suspicious circumstances surrounding their family's deaths and the significant financial inheritance they received. He finds the siblings' current lifestyle and Jin's request for a fortified home inconsistent with their apparent lack of income, fueling his suspicion of hidden activities. He decides to investigate the source of their wealth and the family's past tragedies more thoroughly.
