Come to think of it I haven't hear anyone say anything about it in canon
Onee-Sama!Onee-Sama is a pervert!!Well, it's...Just like fruits.And what's with the stone?——So, what is the matter, Flan?That stone is one of the magic crystals from Flan's wings, puppet master.Eh?And Patchy!That way, once it gets to a certain size, you can remove it.Enough!! Not another word, Onee-sama!!Wow...Flan's wings are rather special, you see.Magic power continually flows out, crystallizes, and finally turns into a magic crystal.