In Yesterday, the year 2020 depicts a unified Korean peninsula where the scars of the past are hidden beneath a high-tech, neo-noir veneer. The setting, known as the "Inner City," serves as a polished urban hub for a joint North-South administration, though the periphery remains grimy, overpopulated, and riddled with crime. The world is defined by advanced surveillance and a specialized police force, the Special Investigations (SI) unit, which utilizes high-tech forensic tools to track a mysterious serial killer known as "Goliath."

The film’s central dynamic revolves around a secret 1990s military project that involved the abduction and genetic manipulation of children to create "killing machines." This suggests a future where the primary driver of technological advancement is clandestine military R&D rather than consumer-facing innovation. Society appears heavily militarized, with the Special Investigations Unit operating with paramilitary authority. This alternate timeline diverges from reality most sharply at its starting premise: a peaceful, institutionalized unification of North and South Korea that had supposedly stabilized by the late 2010s.

Comparing the film's 2020 to the actual year, the most significant missed prediction is the unification of Korea; while the film envisioned a shared capital and integrated military-police structures, the real 2020 saw continued geopolitical tension. However, the film accurately anticipated the aesthetic of the modern smart city, featuring pervasive digital displays and advanced biometric tracking. The biogenetic plotline serves as a cautionary tale about the ethics of human enhancement, reflecting early 2000s anxieties regarding cloning and gene editing that remain central to modern scientific discourse. Because limited retrospective analysis exists for this specific cult film, these comparisons are based on direct visual and narrative evidence from the text relative to historical 2020 milestones.