Ryuuichiro Isaka (井坂 龍一郎, Isaka Ryuuichirou) is the senior managing director at Marukawa Publishing and a supporting character in Junjou Romantica. His lover is Kaoru Asahina and their relationship is titled Junjou Mistake. He features as a main character in an episode in Sekai-ichi Hatsukoi and later in an episode of Junjou Romantica.