The 4th Army Corp was the fourth army service branch of the Zahard's Army. They were responsible for executing the Three Orders point No.2, which is to either capture or eliminate everyone who boarded the Hell Express.
Shortly after they arrived at the 44th Floor not far from the Last Station, Kallavan and the 3rd Division was intercepted by Ha Jinsung who blocked their route by standing in front of them. At first, Kallavan intended to ignore him, but when Jinsung threaten to shoot them down with the El Robina shinsoo cannon, and threaten to destroy The Warship, Kallavan had no choice but to come out and greet his former teacher.
After the 4th Army Corp failed to kill the IrregularBaam, Kallavan, the commander of the 4th Army Corp, was demoted.