It starts off with two young kids. The boy was the crown prince and the girl was the daughter of an official. They meet when Heo Yeon Woo (the girl) enters the palace because her brother was first in literature and her brother's friend was first in military combat. While chasing after a butterfly, as naive as it sounds, she runs across the crown prince who was trying to escape the palace to find his half brother (born from a concubine). They collide and startle the guards causing the crown prince to not be able to escape the palace to find his brother. However, the crown prince came to like her because she was pretty, smart, and unique with her modern ideas. Over time, Heo Yeon Woo reciprocated the feelings and attended the ceremonies to choose the crown princess. At the same time, the crown prince's half brother was also in love with Heo Yeon Woo. He knew her because his teacher was her father. This love triangle later grows to be part of a much bigger scheme that demanded a great sacrifice from the seconds leads (both male and female).
Bo Kyung is the female second lead. She was sent to the palace to try to get married to the crown prince because her father thirsted after power. The daughter was not in on her father's plans but she also liked the crown prince and wanted to marry him. So it was very complicated because she noticed the crown prince's favor to Yeon Woo. She felt neglected but she was also guilt-ridden for many years when she learned of her father's contribution to wiping out Yeon Woo to allow her to get married. I actually didn't hate Bo Kyung that much because the girl was so guilt-ridden that she began to have panic attacks and have hallucinations, I hated her father and the crown prince's grandmother who only wanted to get power. She just wanted love. Plus, in that society, she has to follow her father's orders.
Then through the act of dark magic and a shaman's promise to save the child, Yeon Woo is believed to have died without anyone knowing that her grave was dug out afterward. Yeon Woo loses her memory in this time and follows the shaman. She's nameless and is accompanied by her faithful servant who couldn't reveal her true identity to keep her mistress safe. While everyone believed Yeon Woo was dead, our beloved crown prince married Bo Kyung unwillingly and unhappily. Bo Kyung became the crown princess without much joy because of her guilt and the realization that her marriage was not one of love but of connections for power. Many years pass and the crown prince becomes the emperor and Bo Kyung becomes the empress. In the span of those years, the crown prince remained faithful to his first love and didn't even consummate his marriage yet. Bo Kyung was not loved. For eight years, (I will now call the crown prince, the emperor) the emperor kept faithful to his childhood love and refused to do anything with Bo Kyung leaving her sad and disappointed every time.
Afterwards, the emperor meets Yeon Woo and is shocked at how similar she was to his childhood love. He named her Wol (meaning moon) since she had no name. He starts to fall for her overtime, especially when she became a palace shaman (even though she possessed no powers whatsoever). The half brother of the emperor who also had liked Yeon Woo when he was younger, also began to notice how similar Wol was to Yeon Woo and started liking Wol too. I think the brother was the first to realize that Wol was actually Heo Yeon Woo. The ending was very bittersweet. The turmoil throughout the drama made the ending feel relieving. I just felt horrible for Bo Kyung and the half-brother (second leads). Their love was so pure and loyal. They had no intentions of being part of the political scheme and most were unaware. Yet because they were also a sun and a moon, they had to be gone. I pitied them because they never received love. They just kept giving it to people that never truly appreciated it.
This drama was absolutely entertaining and I would keep coming back to this if I could.