The Legend of the Blue Sea (2016)

All the gods will be leaving before the last rain of doomsday. However, an ordinary human girl unexpectedly puts a dent in their plans to retreat thus causing the world to move towards the unknown. Based on the animistic mythology of the Amis tribe, the gods are no longer willing to bless the land that is plagued with environmental issues. One by one, the gods depart the world they once loved. A human girl discovers that the opportunity to reverse her destiny lies within herself and her guardian. Before the final day of judgment, a love story between human and god unfolds.

Both fantasy drama so if you like fantasy dramas definitely give it a try. It's a perfect mix of funny,sad,musical and romantic elements. The performances by the FL are absolutely beautiful. The last few episodes make you sad specially last episode but if you must know,It's a happy ending.

- Both female leads don't know how the modern world works.
- Both dramas includes friendship and eventually getting to know each other
- The Male Leads let the Female Leads stay at their house until they find the Female Leads' relatives.
- Destined love? They both met before but they don't know.
- Both Female Leads are bright and energetic.
- The Male Leads act mean but actually worry about the Female Leads.

One of our leads is a dumb mermaid/merman arrives in the shore by mistake and the other one is the first person he/she encounters in there.

Both sea-creatures forms a strong bong with that person. They are about humans, mermans/mermaids and overall relationships and friendship.
Sometimes they touch the topic of how we pollute the ocean.

In both they are gready people who want to catch the merman/the mermaid for their own benefits.
In both they are glimpses of the merman/mermaid's past.

In both the merman/mermaid has a supernatural powers and strange urges. It shocks with unusual behaviour as it can't understand the human world well.

The plot revolves around the meaning of life when a young man meets a mysterious beauty who is the incarnation of goldfish.

~~ Adapted from the novel by Ogiwara Hiroshi.

Both dramas have "fish out of water" leads with water-related abilities/worlds who come on land to find their true love. The human they attach themselves to reject them at first but are forced to live with them and teach them about the world, only to fall in love.

The crime part of the story in W reminded me of The Legend Of The Blue Sea
Both are Love story with cute and sad parts as well
(and with their own kind of humour)

Mermaid character meets human, romance follows. They cry pearls which the human uses as money. Comedic moments mixed with serious ones.

Both dramas feature reincarnated lovers meeting again in modern day. In their past life in a historical era, both fell in love with each other but ended up with tragedy. Both couples are given chances to meet and fall in love again in the modern day current life.

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.

The two of them about two lifetimes one in the past and one in the present and they are trying to change the history maybe in a different way but for me i think they are really similar and the both of them are good

These may not appear to be similar, but I was reminded of LOTBS when watching Extraordinary You. LOTBS is more serious while Extraordinary You is fluffier, but both dramas have:
-funny/spunky female leads
-cute romance but with sad/emotional scenes sprinkled in
-parallel timelines (joseon/modern) in which ML and FL were in love. In both dramas the ML is aware of the parallel timeline and tries to change their destiny
-amnesia

This drama is a love story between Kataoka Sakuya, a grim reaper who comes to the human world for the first time, and Mochizuki Nayuki, a woman who lost her father at a young age and has devoted her life to raising her only remaining family—her younger brother. As they meet, they gradually come to understand each other, and slowly, they begin to fall in love. However, a fate that will dramatically change their lives awaits them both…

Both are centered around mermaids, the male leads have sketchy occupations, and there are interspecies romances.

Both are love stories between a mermaid or merman and a human. The mermaid/merman's life is attached to the human.