some illness themes -
90 days of love (warning besides the fact that he is dying they are also blood related cousins and in love)
a thousand day promise (she has Alzheimer's)
autumn tale
sorry I love you
With illness I say 1 Litre of Tears and Taiyou no Uta (drama and movie). Also if you like teen pregnancy 14 Sai No Haha. Also if you are looking for a drama/romance drama I'll alo recoment Innocent Love and Nagareboshi. *.*
Good luck =D
Autumn Tale, Foolish Mom and Mr. Goodbye.
But if youre looking for this kind of theme like Koizora then I can recommend Autumn Tale.
The other two have that kind of theme but on the same time not. Those can you find on gooddrama and drama.net! :)