Seu is a human who defends Mensab in Cave 8, and is never far from her side. He is a Planter, or at least a descendant of them, and has a sword and cape much like a medieval knight. He is much stronger than a normal human, and can easily match most Cyborgs in physical combat.
Whenever Seu is critically injured, Mensab takes him to a machine that can make any object you want. It heals all of Seu's physical injuries, but his memory fades with each use. Despite his mental trauma, he always remembers how to fight.