Recommendations

There's a mermaid in the sea and then she's like a cute one , but it's not a melodrama but its a mermaid story,

Both of these dramas focus on the love life of the children of a large family. In both dramas one of the children is a player, the other has never dated before, and another is going through the hardships of marriage.
Unfamiliar Family and Father is Strange both focus on a secret that the parents of the families have been hiding for years.
Father is Strange is a really cute and fun drama to watch. It goes over the love of siblings as well as the struggle to accept those that you love. It has the added bonus of jokes about homosexuality.
Meanwhile, Unfamiliar family is a little darker. It goes over the hardships of being considerate towards your loved ones. It also shows the hardships of a being a closeted gay.

It's similar again because the Fl's a mermaid and she is crazy and there is romance and comedy . Tags are same Xd Nope

Never Twice and Unasked Family both have FL's that have lost their husbands and are raising a young child by themselves. The ML's for both of these dramas are office workers.
However, Never twice focuses on way more families than Unasked Family does. And Never Twice holds a darker tone than Unasked Family did.
Unasked family is about a woman uncovering the truth about her husband's death while falling in love with the office worker who received his heart (her husband was an organ donor) .
Never twice is about a woman uncovering the truth behind her husband's death while falling in love with the nephew of the man who killed him.
The two premises sound really similar don't they?

These two dramas are both lighthearted, comedic, and cute family dramas with disturbingly manipulative villains who both marry husbands who they love dearly but end up making unhappy. Both of the villains either fake a pregnancy or get a miscarriage.
The main couple in both of these is equally as sweet and aesthetic (bless whoever casted them) and are both love-to-hate couples.
Unasked family and Sunny Again Tomorrow both have families that are tightly interwoven with different connections. However, Unasked Family only focuses on 2 of these families while Sunny Again Tomorrow focuses on 4.
The main couple in both of these dramas has an adoptee as one of the characters (I won't point out who as it might be a spoiler).

Basically the plot devices of both dramas are really similar. And the main couples are really worth the watch. However, both of these dramas have different premises. Unasked family is about a single mother uncovering the truth behind her husband's death and falling in love with an office worker (who just happens to have received her husband's heart during a heart transplant).
Meanwhile Sunny Again Tomorrow is about a (45-ish your old) mother who lost her child 20 years ago searching for her child; unbeknownst to her, her daughter has grown up to be the CEO of a small clothing business and is in a relationship with an office worker.

This is a family drama with a similar feeling to Bad Love, however it's more comedic and lighthearted.
Sunny Again Tomorrow is about a mother who lost her child 20 years ago, unknowingly being her child's main competitor in the fashion/clothing industry.
The romance in both dramas is also similar as in the parents of both main couples are against the two being together. There is also a villainess arch in both dramas and both of the drama's villainesses in the same way. The villainesses also both marry men who they end up making unhappy and they keep on digging themselves deeper and deeper graves. Both of the villainesses are equal in their level of manipulation and blackmail.
If you liked either of these dramas, watch the other one for sure!

It's Similar because In Legend of the blue sea , Jun Ji Hyun is a mermaid and In Swing to sky Hu Bing Qing is a mermaid . They two know nothing as a mermaid in the drama . And Swing to Sky is whole same to legend of the blue sea.

business workplace and love. Characters in their 30s. Older female/younger male. trio of friends who go through troubles together. strong indepent female leads.

older female/younger male couple both in a business working setting. About worklife and romance. Female's family is opposed to younger male.

the concept from ep10-11 in The Great Escape: Season 3 is the same era as Mr. Sunshine, 1920s-1940s ie the japanese colonial period

Both talk about mysterious characters and about......................................................................SPOILER. human cloning.

Trio of best friends making their way through work, life and love. Multiple couples including an older woman/younger male couple.

Similarities
workaholic cold-hearted female business woman who only cares about her work encounters happy-go-lucky guy who also runs his own business. He falls for her first and actively pursues her. Female's personality is caused by trauma from a past issue.

Both dramas talk about moral dilemmas surrounding human cloning and have a quite dark atmosphere. The relationships of the characters are complicated and in some cases obsessive.

one of the main couples is the beautiful charismatic and stubborn workholic female and her 10 year younger playful assistant who eventually fall in love. older woman/younger man love story. Both dramas also have multiple couples: an enemies to lovers and a friends/coworker to lovers story