Kassen

A princess of the Royal Family of Eiattu and sister of Plourr Ilo, Kassen was murdered by rebellious Eiattuan nobles together with the rest of the royal family.

Behind the scenes
Most members of the Eiattu Royal Family had rather long names and shorter nicknames used on informal occasions. It is highly likely that "Kassen" was such a nickname, and thus we cannot know the princess' full given name.