The drama includes the Romance tag, but I think The Romance Tag alone isn't enough to describe this drama.

I say it because where the first half of the drama is indeed filled with cuteness , fluffiness and swoony romance , the latter half is all about the bitter realism of women's lives in a 18th century Palace Building.
And the viewers who come to see the fluffy romance in usual fusion sageuks may be disappointed by this.

It's more like a tragic union of two people from different social classes, who need to fullfill their respective roles,and chained to their respective roles in a patriarchal based society, so that their destined romance becomes a tragedy in spite of their love.



-----*------Spoilers Ahead

YiSan's life was tragic from the start.
He was born into the Royal Family in the Royal successor line as a Royal Grandson.
His life might be the one everyone wanted to live in, but actually not an easy one for himself.

His father( Crown Prince Sado ) accused him of robbing fatherly love from Yeongjo before his death.
His Grandfather ( King Yeongjo ) saw his unobedient son ,Sado in his grandson ( San ).
Noron Faction was afraid of him and against his rise to power, so they attacked him every chance they got.

He needed to look out for enemies and be mindful of his grandfather 24/7 for his whole life.

But San was still the dutiful and loyal Grandson of the Royal Family , strict on himself and groomed to become a capable ruler of his nation.

On his road to become a King, he unexpectedly met a court lady who was intelligent enough to help him .
She was loyal to him and cared him as a human being .
San 's hard shell around court ladies and determination to create a perfect family with a wife from a noble family : all of his beliefs were shaken by this woman.San had fallen in love with the woman who was devoted to him and used her life to protect him.

.......

As for Deok Im , I will describe her as a woman who was too intelligent for an 18th Century one.

As she read a lot of books since her childhood, she was knowledgeable even as a young court maid.

While other court's maids were dreaming of receiving the King's Grace(slept with the King & living the luxurious life as one of the king's wives ), she was the one who understood the burden of being a King's concubine since her young age.
( Fragile life depending on the King's favor, constant power struggles , her title and status wouldn't belong to her anymore, but to the Royal family ,etc )

She was a free spirited woman who wanted to enjoy her life despite her limited freedom as a court maid.

But the Fate didn't allow her even to be a simple court maid and tied hers to that of Tiger Prince, Yi San.

When she met him for the first time, I think she had a crush on him as the Crown Prince 's lecturer ,as most girls of her age would, though she knew she couldn't marry him because of her status as a court maid.

After his hints of confession in the market, she was swayed .
But her feelings were immediately contained after Hong Deok Ro's speech about how unimportant a court's maid feelings were ,apart from herself and after hearing San's determination not to fall for a mere court maid and to take a woman of noble status as his wife during her Coming of Age ceremony.

****Here we need to note is
unlike San, Deok Im was constantly reminded of their Social Status here and there.******

But San was still her master , she needed to help him when he was in trouble cause San's demise would mean her expulsion from the Palace,her Home at least( if unfortunate, death ).

While helping him, their feelings were interwined and she had fallen in love with her master as a man.

------*------

After San got on the throne, everything became complicated.
Their power differences became more apparent cause he was not a powerless heir who needed her help anymore.
The only thing he wanted from her was the comfort and family given by her as his woman.

He was the man with the highest authority in Joseon , everything was entitled to him.

As the word ' lonely at the top ' ,San became more lonely as the King because he couldn't believe his own mother anymore. ( His mom 'Hong' clan is from Noron faction ).

As he felt lonelier, San's desire to take Deok Im as his partner became stronger.
So when she refused his confessions and his marriage proposal, he became disappointed and angry.

****While everyone's having problems with San's behaviors in later episodes, I have no problems with these.

San was groomed to behave like a king since he was young and taught that the court maids were the King's Women and entitled to him.
This was part of his nature and this was the realistic portrayal of what an 18th Century King would be.
( As much as Real life Jeongjo was a benevolent patriarch, he did punish Uibin's maid after her 2nd rejection )

I don't consider his behaviors as romantic either . Only as his nature and not disturbing enough to ruin my viewing of this drama.

*****

On Deok Im's side, as the woman who got the King's affections, she was not only pressured to become his woman but also in danger of being used as a leverage in court politics.

The harder thing for her was her own dilemma.
She was not the young court maid in the library who didn't have much desires anymore.
She loved San and wanted to have him as a man.

Her own dilemma of what to choose ;
Her own precious freedom or the man she dearly held in her heart .

At last, she accepted San's will because she loved him more than her freedom and partly because her freedom was not like it was before and limited by those in the court.
She became a concubine mainly because of her love for San ,but partly it was also because of court politics.

....

Despite becoming partners in marriage ,San was not the ideal partner or hers alone like she always wanted him to be, while she gave up everything just to be with him.

As the one with higher authority in relationship, San failed to see Deok Im 's sacrificial love as a whole picture.
(She might not say 'I love You ' out loud, but she showed it with her choices and behaviours ,but San failed to recognize it because his attention was not on Deok Im alone, but the whole nation .)

On the other hand, he prioritized his role as a King over the role as a husband and
made some choices as a King though he clearly knew these would hurt Deok Im.

Deok Im's Sadness and Resentment slowly built up in this unbalanced relationship ,but moment of happiness with San comforted her.
Her life as a concubine was a mixed bag of disappointment and happiness.

But after the death of her son and her best friend , her husband was busy playing the King for his nation . Her already fragile body was burdened with much emotional baggage and she needed to face that alone.
And well , the tragedy striked at the last moment.


.....
San and Deok Im were clearly in love with each other.

But in the era they lived in, they could never fully embrace each other .

Deok Im wanted San as hers , but he was a king so it would never be a thing.

San was the King ,yet he couldn't give his woman the thing she wanted most , namely 'Her freedom' because the system didn't allow that for the women of the Harem and he needed to live as an example since he was a ruler of the nation .

Unlike Romeo and Juliet, San and DI might not have two families who were enemies with each other.
But the system itself and the Palace became huge obstacles in their love story.