The Great Disaster of Sagami Bay (相模湾岸大災厄 Sagami-wangan Dai-saiyaku?) was the worst Aradama-related tragedy in history which happened from September 23 to 26, 1998. The incident occurred on the coast of Sagami Bay that led to large amounts of Noro being leaked into the sea, which formed into the largest Aradama ever observed. The Aradama landed on the coast and headed north, causing large-scale damage to the city of Fujisawa, which resulted in over 3000 casualties. Through cooperation of the SRRS and the Self-Defence Force, the Aradama was driven to Enoshima. Thanks to the efforts of the select few elites of the SRRS, it was successfully subjugated. Following the event, the aforementioned six elites were labelled heroes.

The ones who vanquished the Great Aradama were Yukari Origami, Ema Kagashima, Iroha Yoshino, Yukina Sagami, Sana Niimi, and Yuzuki Fushimi.

It is revealed that the real heroes of the event are Kagari Juujou and Minato Etou but they failed to destroy the Great Aradama entirely and a part of it survives and possesses Yukari Origami.

According to Richard Friedman, this disaster was caused by the action of humans gathering Noro in one place and attempting to send it overseas to the US.