Kasumi and Rei are both based on the Okinami pattern, but they feature only the lower wave part. While Rei shows only waves, Kasumi has a border with a pattern that became known later on as Sekai.
Kasumi is a Japanese name (quite a few Manga characters bear the name) as well as a few other things. It literally translates to ‘Mist’. I haven’t been able to find the source of the pattern name.