Nexon's popular online tactical RPG, Blue Archive, experienced an unusual security breach on August 31, 2025, when a hacker overwhelmed the game world by flooding it with multiple copies of the anime character Kurosaki Koyuki. Dubbed the "Koyuki apocalypse", this incident resulted in six hours of emergency maintenance to restore normal gameplay. According to Nexon's official statement, the attacker exploited vulnerabilities in the game's content delivery network (CDN) environment settings, which are managed separately from the core game servers. These settings were redirected to an IP address located in the Netherlands, allowing the hacker to alter client-side visual elements without accessing or compromising players' private information. The effects of the hack were striking but ultimately non-destructive: recruitment banners displayed only Koyuki, cafes and other in-game locations were filled with her clones, and the game's information page was replaced with the phrase "Nihahaha," mimicking the character's signature laugh. Additionally, the character Hatsune Miku appeared during the incident, further evidencing the visual tampering. Nexon reassured players that no accounts, game data, or payment information were affected, as those are stored on a separate database with strict server-side validation. The company quickly took Blue Archive offline to investigate and remove the unauthorized content. As a goodwill gesture, Nexon awarded affected players compensation including a 10-Recruitment Ticket, 500 AP, 150 Tactical Challenge coins, 3,000 Expert Permits, 300,000 Credit Points, and a variety of Lesson, Bounty, and Scrimmage Tickets to make up for the disruption. Industry observers noted that while hacking attempts targeting online games are unfortunately common, this case stood out for the hacker’s playful nature and lack of malicious intent. Rather than exploiting financial or personal data, the attacker embraced mischief, sparking a rare moment of chaotic humor within the community. This incident also highlights continuing challenges in securing cloud-based game infrastructure and the increasing importance of robust CDN management. As mobile and online games like Blue Archive attract large, engaged global audiences, developers must continuously reinforce security measures to protect both their communities and their digital assets. Meanwhile, gaming communities remain vigilant amid an evolving landscape of cyber threats, balanced against efforts to maintain fun and fair play. Nexon's transparent communication and prompt remedial action in the "Koyuki apocalypse" have been well received as a model response to a unique cybersecurity challenge.