Both are youth and romance dramas and set in the late 2000s (one is 2007 and the other is 2008). Both dramas are centered around a close group of friends in and out of school.

Both are youth-romance dramas, set in school (and out of school), set back in time (both within the 2000s), and both are centered around a close group of friends

I have yet to watch the drama (Gyeongseong Creature), since it hasn't been released yet, but I already see a few similarities such as:
Genres: Action, Thriller, and Sci-Fi
Cast: Great, Fairly Well-Known
Concept: Humans and Monsters/Creatures
Involves: Investigations

Both share the same Genres: Action, Thriller, and Sci-Fi
Both share a similar Concept of: Humans and Monsters/Creatures in the same world
Both share similar Tags related to: Supernatural

Both share the Concept of Humans and Monsters/Creatures in the same world
Both share the same Genres: Action, Thriller, and Sci-Fi
Both share the similar tags related to: Supernatural

Both share the same Genres: Action and Sci-Fi
Both have similarities with a Concept involving: Humans and Monsters/Creatures
Both have the tag: Supernatural
Both have a Cast that is: Well-known (many popular actors/actresses)

(These aren’t all of the similarities, but these are the ones that I could think of at the moment. I highly recommend checking out this drama if you liked ‘When I Fly Towards You’)

Similarities between dramas:
• follow a group of close friends
• set in the past
• in high school
• romance
• cute fl
• cute, fun, wholesome, and close relationships between friends
• directed by Mao De Shu

Both dramas are set during an older time and in a close, friendly neighborhood. They are about youth, friendships, family, and growing up. They have romance too.