Red Light District
The flower willow for some reason is a red light district. Just imagine a shady red light district, and right in the middle is a flowering willow.
かりゅう
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
彼は花柳小説の有名な著者ですよ。
He’s a famous author of red-light district novels.