Moon Lovers: Scarlet Heart Ryeo

There is similarity betweeen princes in ML and three friends in GF, characters was changing from harmonious friends to enemies in both shows.

When a total eclipse of the sun takes place, Go Ha Jin is transported back in time to the start of the Goryeo Dynasty of Korea during King Taejo's rule. She wakes up in the body of the 16-year-old Hae Soo and finds herself living in the house of the 8th Prince Wang Wook, who is married to Hae Soo's cousin. She soon befriends several of the princes and meets the ostracized 4th Prince, Wang So. Although knowing she should not get involved in palace intrigues over the succession to the throne, she inadvertently becomes a pawn in the struggle, as several of the Princes fall in love with her.

Not too similar except the fact that Lee Joon Gi is the lead in both dramas and the romance of his character and the female lead are crucial in both dramas.
However, I am recommending Flower of Evil to Moon Lovers fans because Flower of Evil is such an underrated drama and more people need to watch it. I know Lee Joon Gi has many fans from Moon Lovers, so I hope his Moon Lovers fans can watch Flower of Evil. Don't undersestimate the female lead, Moon Chae Won may not be the most popular to today's kdrama audiences but she is an acclaimed actress and she has great chemistry with Lee Joon Gi.
As for Flower of Evil fans, it is good to recommend Moon Lovers since it is indeed one of Lee Joon Gi's most popular roles, it's a good idea to watch it for Flower of Evil fans to understand why Moon Lovers fans hype Lee Joon Gi's role in this show so much. And Lee Joon Gi did a great job in this role too.

Both are about a modern day FL who travels into the past and finds herself in involved with at least one prince.

Both female lead were favor, but has sad ending.
Both female lead were kind, beautiful
Both young ming were down jealous, no confidence, palace politic

Both are about a modern day FL who travels into the past and finds herself unexpectently falling in love.

Both are about a modern day FL who travels into the past into the body and identity of another girl.

Both were historical drama.
Both female leads were beautiful.
The main lead were deeply in love
However, ending were sad

In both shows the leads are socially awkward outcasts. They also idolize their popular love interest.

When a total eclipse of the sun takes place, Go Ha Jin is transported back in time to the start of the Goryeo Dynasty of Korea during King Taejo's rule. She wakes up in the body of the 16-year-old Hae Soo and finds herself living in the house of the 8th Prince Wang Wook, who is married to Hae Soo's cousin. She soon befriends several of the princes and meets the ostracized 4th Prince, Wang So. Although knowing she should not get involved in palace intrigues over the succession to the throne, she inadvertently becomes a pawn in the struggle, as several of the Princes fall in love with her.

Sakahira Riku, a first-year high school student, is jokingly pushed on the shoulder by his friend Tasaki while swimming by the pool, and falls into the pool with Mizumura Manami, who is next to him. The next day, when he wakes up, he finds that his body has been swapped with Manami's. Both are confused and try everything to get back to normal, but nothing works. They are forced to desperately exchange information about their families, friends, club activities, etc. in order to play the role of each other.

Both are about a modern day FL who travels into the past and finds herself in involved with at least one prince. Both have the same sad ending.

Both are about the FL traveling to the past and unexpectently falling in love with the ML.
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Both are about a modern day FL who travels into the past and finds herself in involved with at least one prince.

More then anything, because of historical facts. if you got interested in historical events from Scarlet Heart, you should give it a try ( like I did). This drama takes time just after Gwangjong's reign, and starts with story of Gwangjong's son, Gyungjong. There're some more couple of characters that you will recognize from Scarlet Heart.. As well, all the tragedies start because of the battle for the throne...