The Disappearance of the Magical Girl

A kind of monster appears on the earth that feeds on desire. The monsters wreak havoc on the world and become stronger by absorbing desire. At first the bullets could still penetrate the monster's body, but later the monster became immune to ordinary weapons. When people are panicking, magical girls are born. They use actions to purify excess desires and weaken monsters while fighting them. People's struggle against monsters achieved initial victory in two years. However, I don't know when the girls gradually disappeared from the public's sight. Monster attacks become more frequent, and panic and chaos descend again...