The second female lead, who was in love with Yi Yeok in Queen for 7 Days, reminds me so much of Kim Hwa Gun in Emperor: Owner of the Mask, who was also in love with Crown Prince Lee Sun. These two female second leads played a very crucial role in helping the princes get back their thrones, while they ended up with the main female leads that they were in love with.

As for other similarities,

Historical Setting: Both dramas are set in historical Korea, delving into the Joseon Dynasty. They showcase the societal and political intricacies of that era, highlighting the struggles and challenges faced by characters within the rigid structure of the monarchy.

Romantic Intrigue: Both series include elements of romance amid political turmoil. They portray complicated relationships and love stories intertwined with the power struggles and challenges faced by the main characters.

Struggle for Power: The dramas depict power struggles within the royal court, where characters vie for control, often dealing with corruption, betrayal, and the pursuit of justice.

Intriguing Plot Twists: Both series feature plot twists and suspenseful moments that keep viewers engaged. They incorporate elements of mystery and suspense within the historical context, making the storyline more captivating.

Character Development: The main characters in both dramas undergo significant growth and transformation throughout the series. They face dilemmas that challenge their beliefs, leading to personal development and a deeper understanding of themselves and their surroundings.