Not much of a fan in re-watching dramas these days (mostly because of demanding work) but before I re-watched:
Korean:
Secret Garden (once in a 5 years time--2010-2015)
Wonderful Life (1st time in local television + 3 times in the internet)
Queen In Hyun's Man (two times)
Heartstrings (two times)
Pinocchio (2 times, 2nd time only the essential--heartbreaking moments)
Japanese:
Gokusen (I cannot count, but I think its over 10 times--brought a DVD version)
Gokusen 2 (also more less 10 times, seriously cannot get over Yankumi back in those days)
Itazura na Kiss Furukawa Yuki version (2 times)
Itazura na Kiss 2 Furukawa Yuki version (2 times)
Legal High (2 times--2nd time took so much time since I need to pause to read what Komikado is saying, you know the man talks really fast)
Ryusei no Kizuna (2 times--2nd time is for being clear about the details)
Liar Game 1 & 2 (5 times--each times is when analyzing the character development in each characters in the story)
NigeHaji (2 times--simply cannot get over the story--and Koi dance)
N no Tame ni (2nd times-the mystery behing it is so complicated I need to rewatch it to fully understand everything)
Atami no Sousakan (3 times---1st time for the plot, 2nd time for the character, 3rd time for watching cultural and comical references)