Ranko Ando is a 32-years-old single detective who does her job well and has solved difficult cases. She doesn't listen to others and doesn't care what others think about her. However her partner, detective Toshio Ooyama, holds a strong sense of justice and does care what others think about him.
After a devastating earthquake strikes Makuhara the northern part of Chiba, 18 year-old Yamato, leaves to Makuhara to find his friend Kiichi who lives in the area. On his way Yamato meets Takeru, who is also traveling to Makuhara as a volunteer in the relief effort. However, when the two arrive at Makuhara they are shocked to find that the city, which is under government lock down, is intact and is managed solely by children after a mysterious virus results in the deaths of all the adults. Forced to survive on their own, the child leaders must save the city and also fight the government, which tries to hide the truth.
Yuna Yuki is an ordinary second-year middle school student. She gets up in the morning, gets ready for school, goes to classes, participates in club activities, and has fun with her friends. But there is one extraordinary thing about Yuki -- she belongs to the “Brave Hero Club.” What does the Brave Hero Club do? Who is the mysterious being called “Vertex?” Yuki Yuna and her friends’ story takes place in Year 300, Era of the Gods.