Kekkonshiki no Zenjitsu Ni is basically crying porn for people who like 1 Litre of Tears. Perfect character with a family secret gets brain tumour complete with annoying mother. Boo hoo.
I never felt I was watching Karina play a character, more like a vessel for female viewers to project themselves onto. However, I must say at least it doesn't overdo the crying porn bit as hard as Beautiful Rain which probably holds the non-Korean drama record for most crying per minute.
I managed to last three episodes just for Mano-chan.
Unfortunately, her role is very minor.
Personally, I would take Mano-chan over Karina any day.
If you enjoy watching a perfectly nice and bland character battle a fatal disease, Kekkonshiki no Zenjitsu ni is the show for you. I can't critisize Kekkonshiki no Zenjitsu ni for being what it is but it doesn't do anything well to warrant watching from non-fans of the fatal disease genre of which Konna Koi no Hanashi is probably the gold standard. (off the top of my head)