Waza no Tabibito

Humans acquired a perfect source of energy called "Patia", which brought self-sufficiency in food and fuel to all the people in the world. Trade and transportation began to diminish and finally the advance of the civilization terminated. Now the genetically modified plants cover almost all of the lands on earth and obstruct travelers.
Cient, the leader of a fortress city, sets out on a trip to excavate the lost technology "Patia" with his daughter Ruri. When Ruri gets separated from her father, a giant humanoid weapon of the old age attacks her. Ruri is saved by a girl named Tekuni who is traveling around the world training as a "Wazabito" fighter.