To have sum it up from this work- It is assumed those monsters begin from a few cells in one's body which get control unlike others. It tries to know the host's desire so that it can manipulate it to an "eternal dream of happiness" so it can gain control of the brain and be the Commander of the body. But, there's a time when host's desire for happiness is fulfilled, then the monster turns into a cocoon. When it breaks free, it has the appearance of host but completely emotionless. Apparently, as long as the host's desire is not fulfilled, it would have the body of monster. After that humanity part would die. Some scientists assume it could be evolution or nature's punishment. The ending if humanity wouldn't fight and win would be a society of emotionless human looking creatures.
To have sum it up from this work-
It is assumed those monsters begin from a few cells in one's body which get control unlike others. It tries to know the host's desire so that it can manipulate it to an "eternal dream of happiness" so it can gain control of the brain and be the Commander of the body. But, there's a time when host's desire for happiness is fulfilled, then the monster turns into a cocoon. When it breaks free, it has the appearance of host but completely emotionless.
Apparently, as long as the host's desire is not fulfilled, it would have the body of monster. After that humanity part would die.
Some scientists assume it could be evolution or nature's punishment. The ending if humanity wouldn't fight and win would be a society of emotionless human looking creatures.