Outbreak of World war.
Due to human wars such as radiation exposure, bombs, and biochemical warfare,turtles 
and many creatures who were living in peace as well as humans were injured or killed. 

Living creatures tha evolved naturally have evolved too rapidly or become degenerate.
The turtles also lost the shell that protected them. Other creatures also lost their existing 
physical functions or gained functions that were never before.

The surviving turtles barely survive by picking up helmets of fallen soldiers on the battlefield 
to protect themselves and using them instead of their back shells.
After the war, they reproduced repeatedly, but the shells of turtles did not appear again.
As turtles protect their backs with soldiers’ helmets, their bodies gradually change to fit the 
helmet, and genetic modification begins.

Turtles also have symbiotic relationships with other creatures and complement each other‘s 
lost physical functions. Meanwhile, ‘GRAY TURTLE’ evolves for survival.