Tales of Dark River

Both dramas are in same universe.
Tales of dark river is spin off of blood of youth and tells a story about assassin organization that had some parts in original story.

From same author in same universe.
Dashing Youth is prequel of The blood of youth and all of these dramas are in same universe.

The story of both dramas relates to an assassin organization.

Both dramas are Wuxia with stories relating to an assassin organization. Both have great cast too.

Both are Wuxia and Gong Jun is the male lead of two dramas. The two stories relating to a secretive assassin organization.