Reissmann is the chancellor of Caelin's royal family during Fire Emblem: Rekka no Ken. He is only seen during "Chapter 10: The Distant Plains" after Lundgren's defeat. He had been imprisoned by Lundgren, likely for being a supporter of Hausen, but was released after Lundgren's defeat. He met with Lyndis following her victory and warned her that Hausen was critically ill.
Reissmann is also mentioned in one of Lyn's Support conversations with Eliwood, and apparently Reissmann believed that Lyn needed to become more ladylike to attend social events in the place of her grandfather.