The Legend of the Blue Sea

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.

These two both one supernatural lead and a regular human lead for the other.
They both have reincarnation plots as well as villains who were present in their past lives.
In both of these dramas, the main lead is very confident in his abilities.

1)Written by the same writer and she writes the best male leads making our expectation bar very high.
2)The ML has a protective instint toward the FL. He protects her no matter what.
3)Happy ending
4)Family feud
5)Jealous ex
6)The ML/FL keeps getting into accidents
7)Share past(in case of legend of the blue sea,It's much broad)

Supernatural, spunky female lead (ghost in Arang, mermaid in Legend) with a male lead that starts off indifferent but changes because of the female. Both males have to protect the females throughout the drama. Both males are also looking for their mothers. Both have fantasy, mystery, comedy, drama and romance, and both are based off Korean folktales.

Water always is the mystery entity.... for SSL it's time travel and for LotBS is memories. In a sense, they're both time travel and show how love has no time but overall they have the same comedic feeling and "foreigner" trying to get accustomed to life in a new world.

They have the same kind of fluffy feeling in the beginnings and the way Joon Jae has to teach nearly everything about the world to Sim Chim Chung is similar as Louis hardships to get know the world. So in SKL the girl teaches the boy about how to live a normal life and in LOTBS the boy teaches the girl.
One more thing: in Legend of The Blue Sea Joon Jae forgat Shim Chung because she erased his memories. On Shopping King Louis he also forgat everything because he had amnesia.

Maybe am still stuck with Moon Lovers, but you can see how both revolves around history and present with reincarnation of the main characters. If you love destined romance which repeats itself despite the passing time, then you definitely will love this.

Both FLs are mermaids who come ashore and fall in love with the reincarnation of the ML who they were in love with in ancient times.

Time travel. Both strong male lead. Was a high rank profession at some point. Sweet cute, roller coaster journey.

The story line and the genre is completely different. But there are aspects that are similar. For example the reincarnation aspect. Both are used in both dramas.

While in itself being quite different ( Mermaid mystery vs. BL drama) they both share a plot of reincarnation and rediscovering the past memories and the hidden conspiracies around their past selves. I really love both of them a lot and rewatched them several times. If you are looking for something fresh and fluffy, check them out!

Mermaid Got Married is the Splash-like tale of a beautiful mermaid who loses her pearl when she saves high school teacher Dior Cheng from drowning. It turns out she also saved him when they were both kids so there's an immediate connection between the two. Unfortunately, the pearl is the source of her power so she follows him onto land.