He also maintained a deep friendship with Musashi MIYAMOTO, who guarded Katsunari's legitimate son Katsushige (also known as Katsutoshi) as a guest military commander of Katsunari's army in the Osaka Natsu no Jin.
宮本武蔵との深い交友もあり、武蔵は大坂夏の陣では勝成の軍勢の客将として嫡男勝重（勝俊）を守護した。