Princesa Excedente (2014)

Ha Ni is a mermaid princess in the underwater empire, but she falls in love with Shi Kyung, and for him she becomes a human being and begins to live at the In Gyeo House. The house is for people who are preparing to land their first jobs. To permanently become a human being, Ha Ni must make Shi Kyung love her within 100 days.

Both star female leads who are mythological creatures that want to become human.

Supernatural elements

Magic

Female leads appear human but aren’t necessarily humans but supernatural beings

Humor warmth found family

Exaggerated reactions that are used to bring humour. Both main girls fall in love at first sight with a man for whom they'll enter "his own world" to win him over.

-Both main female lead are pretty strong
-Both main female lead likes someone at the beginning
-The guy that the Female lead liked realizes their feelings later on
-Love triangle
-Female lead slowly realizes feelings for other Male lead

Only difference is that the Female lead is a mermaid

In both the Rules of Love and Surplus Princess, a mermaid falls in love with a human. The mermaid saves the man when he falls into the water.

Both are packed with comedy and adult humour (Dasepo has much more though).

They both have a similar comedic feel while the main basis of the plot being on the romance itself. Similarly, you can find both have an interesting love triangle relationships.

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.

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.

They've completely different plot, but they both have a quircky heroine and peculiar secondary character; while Surplus Princess is more on the fairytale and Sweden Laundry more like a normal rom-com, they have a similar feel

Both dramas are really different because one is comedy and the other is melodrama but the stories are similar.
Both lead characters fight for their life and have a mission.

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…

References of GD in both.
Both are funny and a nice short watch compared to longer dramas.
Both have a main character hiding a secret.

Both dramas involve a group of people living together. They're both funny and have great group dynamics. Go Go Waikiki is more nuanced and complex. Surplus Princess is fun and entertaining.