Took me 45 chapters to realize all four of them are named after flowers. Lily, Rose, Thalia, and Lupine. Because they're Sisters for the Goddess of Four Flowers
I mean, Lily and Rose are obvious. I also knew about Thalia, but didn't make the connection because of spelling. And I didn't know about Lupine. Only found out after seeing the x.1 cover illustrations showing them with the flowers of their namesake (except Talia. Those don't look like Thalias).