During the One Year War, Katz was one of the orphan kids that lived in the White Base. He was a little child then but by the time of the war between the Titans and the AEUG Katz is the newly adopted son of Hayato and Fraw Kobayashi. He becomes an AEUG soldier and follow's under Char's orders. He's not truly experienced with War and tends to become punished for many of his actions.