World setting and Lead backgrounds explained (Spoiler)

It is a typical fantasy setting like you may allready know of chinese fantasy dramas but with western influences and of course it has the special korean touch. It is set in a fantasy historical world Daeho ruled by a king of the Go family, where two opposing parties are practicing magic and spells.

• One party that consist of mainly four groups and families/clans the Jang (Cheonbugwan) , the Park (Songrim), the Seo (Sejugwon), the Jin (Jinyowon) and may see themself as the righteous
• The second party (I do not know the name) is practicing forbidden magic like soul shifting (ones soul can take over another ones body), led by some mysterious character called the Danju, and deemed evil by the other party

Now to the lead characters:

Male Lead Jang Wook:
The ML is offically the son of Jan Kang the head of the Jang family but his origins are questionable.
In short, Jan Kang can perform forbidden magic like soul shifting and did so in the past against orders. He is then pressured by the terminally ill king Go Sung to perform a spell, the alchemy of souls, wich was masterd by Jan Kang and to "lend" his own body for 7 days to this king so he may produce an offspring before dying. After switching into the body of Jang Kang, the king Go Sung then visits Jang Kangs wife Do-wha, to produce an offspring (so its a kinda rape). As a result Jang Wook (ML) stepped into the world as his mother dies during birth. Jang Wook does not know of his origins and therefore does not understand why his father (now Jang Kang back in his own body) seals his internal power, forbids him to learn magic spells and shuns him. 

Feamale Lead Nak Soo/ Mu Deok Yi:
Nak Soo is a powerfull assasin for the party which practices forbidden magic. One day she is being ordered by the Danju to assasinate the leader of the Songrim who was present during the slaughter of Nak Soos family. But the assasination goes wrong and she was heavily wounded. Before dying she performs a soul shifting spell (alchemy of souls) in order to take over another girls body. But this soul shifting also goes wrong and Nak Soo switches mistakenly into a weak, blind girls body and takes over her Identity, which is Mu Deok Yi. The blue mark that is proof of the successfull soul switching is not on Mu Deok Yis body as expected but in her eyes. This is the reason why the former blind Mu Deok Yi can see again. Nak Soos own heavily wounded body is then retrieved by the Danju.

Both ML and FL meet each other and Jang Wook wants Nak Soo in Mu Deok Yis body as his master, to learn magic spells, as he recognizes the blue soul shifting mark in her eyes.

You are right, I will change the xiancia part. thank you ;)

Hi there, no I have not planned that. I did that mostly for myself to learn the background of the main leads characters so if you continue to do more descriptions and post it I will probablyly be one of your readers ;) . If you plan on posting something complete let me know and I will gladly delete my half baked description to prevent confusing the readers. You can also use what you can from my descriptions so far.

There is still a mystery about why the blue mark go in the eyes and not on the skin next to the heart.

Thank you for your explanation. Although I do love watching Chinese fantasy shows, I'm usually at a loss for the history and breath of what's happening. I'm just along for the ride mostly, and love the costumes and customs that go along with it. But understanding how this drama here has "western influences and of course it has the special korean touch", makes me realize why I'm so drawn into it. And probably why it's reach is so far. It kind of melds all three, and the outcome is SPECTACULAR!