"Barajou no Kiss" ("Kiss of the Rose Maiden") ongoing by Aya Shuouto
Agnes Yamamoto is afraid of lightning, thunder and her father's last words to never, ever remove the rose choker or else a punishment will befall her. I won't spoil of you what the first consequence is since only the first chapter is available, but the turn of events is surprising and very promising. This one has the flower theme too. Two anonymous visitors recommended this title. Thanks!