Recommendations

They both have: smart female protagonists who dress up as men in the beginning of the story; intricate planning and court intrigue as they battle their way to the top; multiple love interests; etc.
Empress Ki is a much better fighter than Queen Seon Duk as an individual, but Seon Duk was up against a more intelligent foe and had some brilliant planning.

The protagonists of both dramas have somewhat of the same feeling. The drama has to do with crime and investigating. Both protagonists goes out into the field, even though they are not meant to be. For both protagonists, there is a "sidekick", a female character that helps them and is "used" to help solve the cases they are doing. The Female characters dislike the protagonist at first but ends up warming up to them near the end. The dramas both have somewhat of the same plot. If you like one, I recommend watching the other as well.

Both involve friendship and romance among a group of friends in the 1990s. Both with the theme of youth and things they learnt in the process of growing up (e.g. What they lost or gained while growing up, the responsibilities they will have to take up upon turning into an adult)

Both are life dramas focusing on aviation. Both focus on character growth and romance is not the center of the story.

Both are about a group of not very similar girls, who develop a friendship. There is a lot of mysteries surrounding one of the girls in both shows. Both are funny and dark at the same time and cover controversial topics. I believe you'll like Seonam if you like AOY and the other way around.

- both have a smart female lead
- both male lead are prince who became king
- both male lead in this dramas, only love one person (stick to one)

Both dramas are about a mermaid/merman and human falling in love.

In both dramas the main male and female meet at a school program. And both the male lead is very famous in the school.

Both involve the process of friendship developing into romance. One of them used to have a secret crush on the other in the past and yet did not manage to work it out.

Both involve love, friendship and family interactions in the past (1950s-2000 in The Story of Time & 1995-present in A Good Day).

Both are about the friendship, family and romance in the neighbourhood set in the 1980s/1990s. Both female lead has three different guys surrounding her-one who likes to badmouth & bicker with her; one who has a secret crush on her; one who has good looks and results (likes the female lead in a Good Way but not for the one in Reply 1988). Lastly, there is also a guy who jokes a lot in the neighbourhood.

Both are about "Contract Marriages". Both start off the relationship because of its mutual benefit. They eventually learn to Love as they face the trials and tribulations of doing life together. Nigeru wa Haji is more light hearted while HapiMari is more dramatic, but both have their really cute heartwarming and funny moments.

Rich arrogant guy who always gets his way vs. Headstrong stubborn common woman who stands up for herself. Both are good romantic stories and both have really handsome lead actors (RMPW - Shun Oguri and HapiMari- Dean Fujioka!!)

In both, the main female lead mistakes the male lead for being gay.

In both, the main lead mistakes the other for being gay. In Heartbeat Love, the female lead mistakes the male lead. In Down with Love, the male lead mistakes the female lead.