A calm and wise duke, who is seen by many to be the likely successor of Ajman as clan lord of Tytania. Of all the dukes it can be seen that Jouslain prefers peaceful methods the most. He shares a unique long-standing friendship with another duke, Aryabhata, and is often the object of Idris' frustration. Jouslain's character is being explored more than the other dukes in the series, mostly through interaction with several characters who appear to be dear to him, most notably Aryabhata, Bal'ami, Francia and princess Lydia of Elbing.