First of all there's no such thing as J-dramas which fully focus on romance and I think that's the charm of Japanese dramas.
Ooops Edit:
That being sad I will recommend you some light romatic dramas/films if that's what you're looking for:
Dramas:
Love Shuffle: My top recommendation for you: it's light, mature, romantic and funny.
Rich Man Poor Woman: A fun rom-com.
Hana Yori Dango (if you haven't seen it yet).
Nodame Cantabile: it's a musical romantic story.
Buzzer beat and Pride: Romance mixed with sports.
Sprout: fluffy and cute.
Kimi Wa Petto and Proposal Daisakusen (although I didn't like them but they were sort of romantic).
Natsu no Koi wa Nijiiro ni Kagayaku: it was romantic but it's older woman-younger man relationship.
Yamato Nadeshiko Shichi Henge: There is love interst but it wasn't fully romantic.
Otomen and Yankee-kun to Megane-chan: School romance.
Switch Girl: there's love interest and sweet scenes but it's not fully about romance.
Zettai Kareshi: if you're interested in human-robot love.
Films:
Kimi Ni Todoke: Innocent romantic story.
High School Debut: A light fun rom-com.
Paradise Kiss: Fashion and Romance.