Flowers (SPOILERS)

Jeile names the girls he likes each with the name of a flower he thinks suitable for them. Such as lavender, rose, but most evidently the mountain lily maiden!

Moutain Lily
Why he names her that in the first place is because he sees that Airi is not afraid to face difficulties. In order to get what she wants, she's willing to storm all weathers. As from the name of the flower, you can guess that this lily survives on rocky grounds. What Airi faces later on in Merupuri is just as bad (or worse). Maruru further explains that its fragrance spread far and wide, making people turn heads. In the case of girls, it's probably her beauty. (She adds that Airi isn't worthy of the title) Initially, Jeile tells Airi that he plans to change her into a Moonflower (please correct me if it's otherwise) since come nighttime it will spread its sweet smell. Otherwise in courtship terms, dangerous pleasure. But that doesn't happen since Airi insist against all his pursuits.

Rose (White and Pink)
Jeile's favourite flower. However, in this case, both Jei and Maruru claim their titles. This is probably because later on, they become his closest people. Jei claims the White Rose and Maruru the Pink Rose. Symbolically, the White Rose represents innocence and purity (much like Jei is). The Pink Rose represents grace and gentle love (somewhat like Maruru is). But to just touch the surface, Jei's overall appearance (eg. tone/shade of hair, skin) is whitish and Maruru is pinkish. You could see it as their favourite colour too.