Miman City (1997)

Original title: ぼくらの勇気 未満都市

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.