Bokurano

"Bokurano" is a Japanese manga series written by Mohiro Kitoh. It was serialized in Shogakukan's "Young Sunday" magazine from 2003 to 2005. The story revolves around a group of children who discover a mysterious robot they are tasked with piloting. They learn that each time they control the robot in battle to fight against other giant creatures, one of them will die as a consequence.