Peng Xiao Ran is the main actress in both
There’s a lot of angst and tragedy in both
But more importantly, both series are somehow similar and yet different : in both, the female lead falls for the king/prince of an enemy country who ruins her tribe and she ends going to live in the enemy country. In both, even though the prince/king loves her, she can’t forget how he ruined her kins and country. Also in both tv series, the male lead (king/prince) also causes the ruin and death of the princess
What makes it interesting is that in both series, Peng Xiao Fan’s character lives in VERY similar settings (the tribes of both female leads are almost the same ; there’s also a killing-wolf scene in both series so I couldn’t help but think that SJFY’s writer willingly did plenty of winks to GMP) and in both series, there’s a princess who gets ruined by the male lead and has a devoted female friend who’s her lady companion but she plays a different character : in GMP, she plays the naive, innocent and pitiful princess who gets ruined by the male lead but in SJFY, she plays the devoted, smart and badass best friend who devotes everything to the princess and then gets her revenge on the male lead. So watching SJFY is like watching her character in GMP getting her revenge on the evil male lead and becoming badass !

An amnesiac female lead who’s been harmed by a greedy/jealous/psychotic female character who wants to steal her everything and as a result of her accident and amnesia (caused by the villain), she goes live with the male lead

An amnesiac female lead who’s been harmed by a greedy/jealous/psychotic female character who wants to steal her everything and as a result of her accident and amnesia (caused by the villain), she goes live with the male lead

-Républican Era
-Revenge
-The female lead thinks that the male lead killed her dad
-Angst between the leads

-Republic of China
-a mix of angst and love between the leads
-Revenge (much less important in SIF though)
-a second male lead who’s sort of her childhood sweetheart/first love

-Rebirth
-Ancient China
-Revenge on a jerk ex-husband who is king
-realizes that all along, there was a sweet young man who loved her silently

Different setting and countries, but in both
-the two leads come from enemy countries, with the male lead’s country submitting the female lead’s
-for this reason, the female lead hates the male lead at first
-she also has a lover at the start of the series
-despite her hatred, the male lead is crazy in love with her
-but she eventually gets won over by his devotion

Koo Kum is much more tragic however. Prepare yourself for a River of tears here !

A man who rebels against an abusive and corrupted system by going against the law and uses a secret identity

- A male lead who starts off as a selfish man who only wants to survive and goes through a lot of changes, and eventually secretly involves through the resistance
- A female lead who despises him at first and is involved in a resistance movement
-It’s about the same timeline, but in different countries, with a rebellion happening
-The mâle lead and his sweet, innocent best friend eventually become enemies, notably due to their love for the same woman and a pledge of revenge from his best friend who turns into a psycho

Both dramas reunite two actors, Huang Sheng Chi and Ma Xin Yu. However, Mountains and Oceans is quite darker (especially in the last episodes) and the two actors have very different parts in the two dramas :
-in Believe in Love, Huang Sheng Chi is the male lead and Ma Xin Yu is his sister, a spoiled noble lady
-in Mountains and Oceans, He’s the second male lead with a tragic fate while Ma Xin Yu has a much more important part, the second female lead and villain of the story who gets consumed by hatred and envy for the female lead and that you will definitely hate to the bone (but her performance is stellar !)

Both are focused on a villain and compare her to a « good girl »
(Lhong Fai is much darker however)

Same author
The same « love and intrigues » atmosphere
We also have two couples who kinda exchange their partners