Cleo is a 12-year-old mech pilot who looks more like an older teenager which her friend Lee makes fun of. She's a quick learner, but can be very clumsy and is somewhat of a slow thinker with other things. She states that her positive skills are cooking, laundry, and keeping watch without getting tired. She and Lee graduated from military school after 2 years, when it ordinarily takes 6 years.
Lee later commits suicide to prevent being captured under the belief that the enemy are barbarians, but Cleo believed Rygart killed her and initially wanted to kill him. After this, she meets Rygart in battle and shows a surprising amount of skill contrary to how she was before, almost fighting off Rygart. She is defeated shortly after securing Zess's escape and taken prisoner, where she is treated very leniently and shares a room with Sigyn. She initially tries to escape by securing Sigyn's gun and tries to kill Rygart, but fails because the gun actually had no ammunition. She befriends Sigyn and doesn't try to escape afterward.
