different plot but both positive, (fantastic is also sad at times because of cancer subject, but same time funny), realistic dramas with real characters and relationships.

also, very similar love triangles which becomes lovely bromance - (spoilers:) when I watched HCCC I thought that I've never seen triangle like this with rival men with so healthy relationship, respect and becoming friends, but then I saw same in Fantastic, even sweeter bromance which started after love triangle. In both dramas SML is very good guy who can see when his feelings are unrequited (though in both dramas FL first liked him) and move on, like it would be in real life and healthy relationships, he can be real friend with FL and ML too and ML very much likes him, they form soo lovely bromance.

not very much similar, but both dramas have very healthy positive and funny vibe (though Fantastic touches very negative subject and has sad parts it still manages to be positive drama), realistic relationships and characters, multi characters and still quite 3d all of them, without unrealistic villains (though Fantastic has very pad people as one family but still realistic ones), primitive cliches, healing...
there are no annoying love triangles, I mean it is in both drama but very healthy when SML and FL are reall good friends without broken hearts.

both are really good dramas, with one look not some new or extraordinary plot but really good watch, dramas that enjoy you (and I's saying it when 80% dramas are boring for me after 5-6 episode)

both dramas show entertainment industry and real lives / relationships behind dramas;

both dramas show quite realistic relationships / romances (TWTTLI is more realistic, Fantastic in more entertaining and good watch), without endless misunderstandings and primitive cliches.

both dramas have high class actors.

Both are really great action/crime dramas that also involve romance, though Cruel city hasn't romance tag, both dramas have romance as side story, but in K2 it was weak part, when romance in Cruel City was great, realistic, mature and hot, with amazing chemistry )))

both dramas have politics and complex relationships (when you don't know who is enemy or friend), very catchy plot and never boring/dragged. K2 has more high society's politic/corruption/business/secrets vibe, Cruel City - politic/corruption/mafia/undercover cops.

in both dramas ML is star of the show, but other characters are also 3D and really good. Plot and story lines are intense, reach and complex, with twist and turns, unpredictable and interesting till the end.
ML in both dramas is super badass, smart (Cruel City's ML is smarter) and physically strong with great fight skills; Also quite anti hero type, especially in Cruel City.

in both drama there is older SFL (practically equally FL, in K2 I would say she is more main than younger FL), who is very badass, strong woman and is interested in ML.

FL/love interest in Cruel City is much(!!!) better, she is strong badass girl.

K2 has more and better fight scenes (somehow even too much, like ML is superman but still great watch).

Cruel city is more dark!

it's already recommended, but I want to add: there are many body/gender swap dramas/comedies, what makes this 2 dramas really similar and really special - AMAZING FEMALE LEAD!!!! in both dramas actress was soo great to deliver really unforgettable character... if you liked one FL you will like other!

both dramas very funny with great side characters. Plus "Come back mister" has Rian who was amazing in this role!!!

tearjerkers about professional killer who hides his identity falls in love with girl but because who he is can't be open about his feelings

one is movie and more dark but they both have:
student who loves/is obsessed with her teacher,
practically unrequited love but connection and caring, learning much from each other, somehow saving each other.
very similar endings, even FL in rain and... same )))
very good acting and chemistry between characters.

quite different vibes and atmosphere but similar relationships:

in both dramas: 2 boys and girl are close friends from childhood, they were together in good and bad times, supported each other in hard times, always together in and out of school. Girl secretly loves one of the guys (ML) and another guy loves her.
But things change when another girl comes in picture and ML develops feelings to her. Their friendship changes, ML changes...

though both dramas are about high school teens but "Tempted" has more mature vibe and somehow little dark.

p.s. both dramas have light sexy undertone (in "tempted" it's more in "3 friends part" and friend female/ML relationship, in "Kinkyori Renai" it's more light and related with sexy second female (who came later in picture). Overall both dramas have one sexy female )))

very same feel while watching, small and big details are same.
also infidelity and complicated love triangle-squares between unexpacted people.
same level sexual content

one is movie another tv series but with many similarities:
*older man/younger girl
*high school student/her teacher
*ML/teacher is also her uncle's friend / so sometimes they meet in house too
*there popular guy in school (in "Daytime" he is ML or SML) who loves FL too
*teacher can't show his feelings because she is student

Both really good watch and good chemistry between leads ("Hello Mr. Right" is tv series so there is more screen time and developed chemistry, but for movie "Daytime" is also capacious and fast paced).

in Both dramas:
**Mystery/romance and even crime dramas
**Very similar MLs (it's main similarity of these dramas). mysterious and very charismatic, dark lonely antihero type ML, whos past is secret/mystery and also trauma for him. He is quite playboy, playing with girls feelings while not feeling himself anything, lying them, not regretting causing pain for girls who love him. He doesn't care much about anything, about material or even not material things, it's very hard to know what happens in his head or heart. It's very hard to make him feel anything, especially love.
**Though he is so closed type guy, from first view some may think he is very flirty and even funny, he is that way with FL too.
**FL is interested, intrigued and attracted by ML, wants to know more about him, support him... he opens up with her more then anyone (but still not so much, especially in "Piece")
**While drama develops, opens secret past of ML, overall his secrets and mysterious personality - is he so dark/guilty or not? is he killer or not?

Overall "Smile has left your eyes" is much (!) better and another level drama, "Piece" has this vibe and good details but isn't executed (or story isn't written enough good) as well... but these similarities is there and ML's really are very similar.
#So after Pieces it will be great to watch this great Kdrama (which has original Japanese version);
#After SHLYE you may enjoy with some similar vibes (but not expect same level drama).

Teache/student, older woman/younger man relationship.
both light nice watch with sweet ML who chases FL first.