Recommendations

Both have ....

-same writer
-Kurashina Kana <3
-some suspense plots
-(very) depressing tone in the start of series, but gradually become more hopeful
-somewhat unique and beautiful ending

Both dramas deal with a father's involuntarily thrust into single parenthood. The dramas also shed an insightful light on Japanese family dynamics - how Japan's brutal corporate culture & rigid adherence to gender stereotypes can test the bonds of marriage. If you love bromance, esp between fathers and sons, these dramas are golden. Kazoku has a better ending if you're a romantic at heart, but both dramas are well worth the watch.

Okay, these 2 dramas are have completely different plots, but it will give you the same vibe, since I found some similarities between them: time traveling, same kind of male main role's personality (calm, calculate and 'rigid'), same kind of female main role (cheerful, reckless, annoys the male lead a lot!!), the limited time living in each other's world and also the good fighting evil plot.

If you were looking for romance younger guy-older woman [and noona is interested in other guy], you should watch Flower Boy Ramen Shop. The topic is quite different (FBRS is romcom), but they have something in common.

School, bands, music, love :D If you like this in Heartstrings, you'll probably like Shut up: Flower Boy Band :D

From the same writer. Both are intense drama that deals with a fight for justice against people on higher-ups(politics,judiciary,business). These drama shows how can a powerful person can bend and control law for their own welfare. And how a person can be blinded by money that leads to betrayals.

About childhood girlfriends growing up and living their respective lives. Friendships, relationships, heartbreaks etc. Both are nostalgic.

both are romantic comedies that show a funny and sweet clash between traditional country clan life and city life, with a leaning toward preserving tradition.

There is the same concept of a student following the aspect of being a detective. Yamada Ryosuke is also one of the supporting student detectives, and there is a similar amount of suspense.

Both: are comedy mixed with melodrama (although I think BotC is a bit more dark and KMHM is a bit more cornball), have people doing dirty deals to try to inherit money/power/family business, feature a sibling-like relationship between the leading lady and the 2nd lead male, have a mystery surrounding both the leading lady and the leading man, leading men have trust issues due to people always wanting to take advantage of them for money, are well done.

Both star leading actress Choi Kang Hee. Both deal with a social phobia that stems from a repressed memory and trauma. Both have adorable funny leading men and even more handsome 2nd leads. Both have tender moments and upbeat endings.

Same story - Guy has been loving her friend for a LONG time but stayed as a friend.

Both movies have the lead girl lose faith in friendship and begin to use it as a tool for their own lack of love and greed.

-Both about a cofee-ya master who helps their customers to solve their problems.
-Both cofee-ya master have somewhat a bitter/dark past
-Both have a sentimental feeling lingering with the coffee smell ...
-Both have one or two cute eye candies :p

Yasashii Jikan is more like a healing - slow pacing - slice of life - nature scenery drama; and Kohiya is a more normal type.