Klein is the leader of a mercenary group from Etruria. He hired Thea and her squad of pegasus knights. His troop is stationed in the Western Isles when Roy's army arrives there. Klein receives orders to enter a battle against Roy to protect the villagers. However, he is persuaded to switch sides by either Roy or Clarine, and then convinces Thea to do the same. He is very fond of his younger sister, but still considers her to be young and inexperienced, and does not hesitate to scold her when he thinks that it is needed.
After the war, Klein becomes an ambassador of Etruria.