Heart of Loyalty (2021)

Same director. Same type of vibe. There is a mystery element and otp don't like each other at first.

In the early episodes of RFY, the relationship between the main couple is very similar to the secondary couple in HOL. The FL vs. SFL are princesses being forced to marry a prince of another kingdom, and the ML vs. SML is a guard of lower status who initially refuses to admit his love for her despite fighting and risking his life to protect her.

Both are mystery/investigation dramas in a historical setting with the couple solving cases together.