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Both are versions of Itazura na Kiss but though they follow the storyline, both don't feel like remakes at all.

Both have antagonists that do REALLY shitty things, love triangles, and are based in school.

A lot of intense feelings. The family support is one of the main points.

Both are school themed dramas, with great friendship and cute romance.

Both dramas' female lead falls in love with the most popular guy at school (the male lead).
One of the various differences: the male leads' personality (in PK he's more rational).

It's also high school drama with romance (with great chemistry!)
Shut Up... is not about becoming friends, like Cheer Up, but it's about saving friendship. But characters in both dramas face the difficult situations and try to solve it together.
And bromances! :D

Triangle is about brothers finding each other after years and the most powerful one is a gangster. K2H is about a prince learning to steer through danger and politics. Two very different dramas. In Triangle, the lead turns from a pitiful, poor, and powerless gangster to the most calculating, powerful one. He steers his people through danger and comes out on top. By the middle, there is no one who doesn't feel apprehension when they hear his name. In King2Hearts, the degenerate playboy prince transforms into a smart, respectable, highly admired leader. Also, in both, the leads were called 'trash' in the beginning.

JaeJoong stars in both. Triangle was about him (not so) covertly taking over a city and a business. Spy - he worked for his country. Triangle was better IMO

IPA is also a Spy drama. Parents have a prominent role in the drama too. IPA is comedy though.

Crows Zero is Parent Story And Have More Violent ...
Shun Oguri and Takayuki Yamada are Much Better

Both Have Same Story But Minami-kun no Koibito Season 3 is Older.... And It Have .... Ninomiya Kazunari

Both stories of parents when their child is sexually assaulted. While Azooma focuses on the pain of a mother dealing with the fact that there is no justice for her child, Hope focuses on the family's way to recovery and the utter hopelessness the parents feel about their child's suffering. A seriously heart wrenching movie that will have you in tears.

Similar stories with two girls from different backgrounds changing identities. A girl from a wealthy family loses her memory while another one consciously deceives everyone. Male lead and female lead met in childhood. Male leads in both are great (their characters).

Both dramas has the same theme where in the main lead is a genius who is good at solving serial killer criminal cases. Although there are differences in the story line, there is still quite some similarities. I wouldn't want to spoil any details since it's the mystery that makes both drama really good, so I'm leaving both comparisons for you once you check it out.

Highly recommending both series for those whole love mystery, suspense and psychological drama with bits of dark humor.

-Both are high quality historical dramas with solid plot. (Nirvana in fire has better plot.)
-Both dramas are about getting justice/revenge.
-Both have strong, smart main heroes.(main heroes uses their brain instead of their fists.)
-Both have a little romance. (it is not the main focus and Empress ki has more.)