Kosei Hoshimi, a young warehouse worker, stumbles upon a mysterious amnesiac man secretly devouring his yakisoba. When the man suddenly takes off, Kosei's pursuit lands him right in the middle of a kaiju attack tearing through the city! Witnessing Kosei's compassion for a girl in the shelter, the amnesiac resolves to shield the city from the kaiju, and a crimson light ignites within him!

The amnesiac man declared his name: Omega. Kosei brought him back to the warehouse, and they start living together. Though Omega's past remained a mystery, the two ventured into the forest, hoping to uncover the true nature of the kaiju reported on the news. It was within this forest that their path crossed with Ayumu Ichido, a biologist. Kosei introduced the amnesiac to Ayumu as Sorato. The three began working together to search for the kaiju.

A kaiju appeared at a construction site deep in the mountains. Soon after, it suddenly died, but the reason is unknown! Ayumu and her junior team member, Yuta, go to investigate in the mountains. Another kaiju of the same species appears there and chases them until they are completely lost... Then, the kaiju begins to advance toward the city with unstoppable determination. Where is it going, and why?