My Life Soul Is Actually a Seed?

Due to some changes in the world, a monster called the Nuclear Beast appeared, and thus blood souls appeared. They are derived from the history and legends of various countries. Every child who awakens at the age of 12 has a chance to possess them. When the ancient heroic souls fight with the Nuclear Beast, and when every hero is willing to shed the last drop of blood for his country, can you stop and read their stories?