Great Hinamizawa Disaster

The Great Hinamizawa Disaster (雛見沢大災害) was a catastrophic gas leak incident in the village of Hinamizawa. The village's entire populace was exposed to a mixture of hydrogen sulfide and carbon dioxide and was completely wiped out overnight. The gas leak resulted in the permanent closing of visitation to the village.

The Great Hinamizawa Disaster does not happen on a specific day in each fragment, its occurrence ranges from June 21 to June 26.

The Great Hinamizawa Disaster first appears in in, however it can be assumed that the disaster occurs in the preceding chapters  and  shortly after each story concludes.

The Official Story
The official version of the events, as per the reports of members of the Japan Special Defense Forces (JSDF) states that volcanic gas composed of hydrogen sulfide and carbon dioxide was released from Onigafuchi Swamp. The gas spread through the village, killing everyone while they slept. The JSDF removed the bodies, quarantined the area for almost 20 years, and covered Onigafuchi Swamp with thick concrete. The event remains ruled as a natural disaster.