Kain (カイン, Kain) is a Japanese manga series written and illustrated by Tooru Uchimizu.
Kain is a story about a blue-eyed boy wandering the countryside. He happens to be in a town controlled by "kidoushi." These kidoushi are people from the newborn country of Ren, who have a machine in their body, giving them power equal to an army. The power of the kidoushi is determined by the amount of gigai (the machine) taken up in their body.