Both have Lesbian romance, they are both in the gl genre. They both have a combination of gl romance and a mystery, investigation of murder/death.

Both are set in a similar time period. Both have a lesbian relationship in them although in Couple of Mirrors it has been censored, but a lot of their relationship still remains. Both have a strong female lead that goes against tradition.

Both are a lesbian romance. Both have a lead that is a Princess who falls in love with a woman in a historical setting. social rank and tradition bars the love between two women.

Both have a same-sex romance, manner of death is a bl, Petrichor is a gl. Both have the same screenwriter. One of the leads in both series is a doctor. Both series are about investigation of death/murder combined with some romance.

Both are a lesbian romance. Both have the same actors. Both deal with the relationship of a woman that is a "commoner" and a woman from a rich/royal family. Both have a forced marriage to a man. Both have a happy ending.