Why Ji Kang Woo changed the ballet? It was random...?

Well, I don't think so. I simply adore when script has some hints and surprises for viewers. (My last drama like that was He is Psychometric and I can truly recommend it to you because of that reason.)

(Now, we are on episode 8 (4 in 1 hour rule which I will use here). I will be regularly updating this post. It contains my interpretations, theories and suspicions. I'm really curious about you thoughts, so please reply me if you want to. ♥ )


The change of ballet:

In episode 2 (4) Ji Kang Woo appeared on corps de ballet rehearsal for Swan Lake, openly criticizing its happy ending. In second scene, we could seen that he changed it for "fresh, never seen before version of Giselle" with Yeon Seo as the main ballerina.


Ji Kang Woo's story:

At the end of episode 4 (8) we've seen small, but important fragment of Kang Woo's story with his dead lover and the fact that he was, or is an angel. 


Giselle:

Let me introduce you to the story of Giselle with a few different versions of it and my comments with subjective interpretation in the case of Angel's Last Mission: Love.

The first act (in my opinion mostly important to  of ballet Giselle tells us similar story to bit of Kang Woo's life we've seen in drama. The second act in his existence  happened analogical to the Giselle, still continue or there is completely new, third act (invented by his dreams and desires, for example with Yeon Seo by his side, whom he is completely obsessed). 

Also, the whole story can repeat with Dan and Yeon Seo. This is the most interesting part, but I will refer to that later. It gives a whole new perspective on ballet's actual meaning in the drama.

What's more, I can see some of Giselle in Ni Na's personality. I'm curious how her character will develop in drama.

Giselle has a few versions with some different specifics. I really encourage you to read various adaptations. You can create a lot more of theories and perceive this tragedy a little bit differently. I will add some links at the end of this post.


The story of Giselle significant for Kang Woo and his lover:

I act

"The peasants of a Rhineland village are celebrating the vintage festival. A young nobleman, Prince Albrecht, disguised under the name of Loys, (reference to the drama: Kang Woo's lover most likely didn't know about his real idetity) pays court to a girl named Giselle, who reciprocates his love. Giselle is happy and pays no heed to the advice and warnings of her mother, who puts her on her guard by telling her the story of the Wilis, the maidens who died before marriage and who, transformed into spirits, lure the men whom they encounter by night and compel them to dance to death. The gamekeeper Hilarion, who suspects Loys’ true identity and is jealous of him, awaits the propitious moment to get his revenge.

Meanwhile a party of nobles who have been hunting arrives at the village, in attendance upon the Duke of Courland and his daughter Bathilde, who is engaged to Albrecht. Giselle confides to the young lady that she has fallen in love. She receives a wedding present, but Hilarion chooses this moment to appear, revealing that Albrecht and Loys are the same person. The prince cannot deny it. Giselle, who feels betrayed in her most cherished and pure sentiment, goes out of her mind. In a wild dance, she tries to kill herself with Albrecht’s sword, then she goes mad and dies of a broken heart." 
(and this is the scene we've seen in the drama, at the moment we don't know how Kang Woo lover actually died)

 (source: www.qpac.com.au)

II act

"Giselle’s mother has visited her daughter’s grave and returns home after dark.

Myrtha, the queen of the Wilis, appears surrounded by her subjects. They all welcome Giselle as one of their own. The Wilis, ghosts of young women who died after being betrayed by those they loved, haunt the forest once night falls. Seeking revenge, they cast a spell on any man unlucky enough to venture into the woods, making him dance himself to death.

Myrtha and the others disappear when they hear footsteps approaching: it’s Albrecht, in mourning, bringing flowers to Giselle’s grave. Giselle appears to Albrecht, who realizes that she has forgiven him his falsehood.

In the meanwhile, the Wilis have found Hilarion. Intent on his death, they lead him on a mad dance, but end up tiring of him and abandon him in the woods.

When Albrecht discovers the presence of the Wilis, Myrtha gives the order to take him into the forest. Sacrificing herself for the one she loves, Giselle dances until sunup to save Albrecht. The glimmer of dawn soon forces Myrtha and the Wilis to flee. Giselle, through this sacrifice, succeeds in freeing Albrecht. In peace, she disappears forever." (because of the girl's sacrifice, Kang Woo can live)

(source: https://mag.grandsballets.com/en/magazine/texts/synopsis/ )


The story of Giselle significant for Yeon Seo and Dan:

And now, please read this story in different context. We can interpret Hilarion as Kang Woo.

Prologue:
Hilarion, the village gamekeeper, is in love with Giselle. She doesn’t share his feelings, however, being secretly in love with another. Hilarion struggles to get over his one-way love, but is eaten up with a jealousy that dictates his actions and his life. 


I act:
The peasants return from harvesting, while the village girls have gathered blooms in the forest for the Flower Festival.

Duke Albrecht of Silesia arrives with a bouquet of daisies for Giselle; he has put aside his sword to assume the look of a peasant and not reveal his true identity. He waits for Giselle at their usual meeting place in the forest. Seeing her arrive in the distance, he hides to try and surprise her.

Giselle, delighted with the flowers brought by Albrecht, twice takes a daisy to question Albrecht about his love; each time, the answer is disappointing. Albrecht, in order to please her, delicately plucks a petal and reassures Giselle of his love. Hilarion surprises the two lovers and questions them about Albrecht’s identity, which he does not know. He openly displays his jealousy and confronts the Duke of Silesia. Albrecht, momentarily confused, forgets his peasant appearance and brings a hand to his sheath, in so doing betraying his status as a nobleman.

When the villagers return for the festivities, Giselle introduces Albrecht to them. During the celebrations, she has a weak spell that gives her fiancé a glimpse into the fragile state of her health. Giselle at that moment has a vision of a being all in light, Myrtha, and is disturbed by an apparition that only she seems to have seen.

When Giselle recovers from her weakness, Albrecht sees the Duke of Courland and his court arriving in the distance. He leaves Giselle without explanation. Hilarion, who has remained in the background, discovers Albrecht’s sword and understand who he truly is. He vows to announce the truth to Giselle at the right time.

Bathilde, the true betrothed of Duke Albrecht, arrives with her father, the Duke of Courland. Looking for water, she comes upon Giselle and her mother. Bathilde asks the latter if Giselle is engaged, to which she replies in the affirmative. Dazzled by her beauty, Bathilde offers Giselle a necklace and asks if Hilarion, who has nodded off close by, is her intended. She answers no: her fiancé has taken himself off.

In the midst of the Flower Festival, peasants and friends launch themselves into a joyful dance. Albrecht and Giselle try to be alone somewhere. When they think they are, she finds the courage to kiss him – under the worried eye of her mother and the jealous eye of Hilarion. In his anger, the latter reveals the sword to Giselle, making clear Albrecht’s identity.

Bathilde and the Duke of Courland, back from their walk, overhear the conversation. Seeing the weapon, Giselle questions Bathilde, who confirms that it is indeed the sword of Albrecht, her fiancé. Giselle understands Albrecht’s lie, and is devastated. Madness overcomes her, and the heart in her weak constitution ceases to beat. Giselle dies...

II act:
Giselle’s mother has visited her daughter’s grave and returns home after dark.

Myrtha, the queen of the Wilis, appears surrounded by her subjects. They all welcome Giselle as one of their own. The Wilis, ghosts of young women who died after being betrayed by those they loved, haunt the forest once night falls. Seeking revenge, they cast a spell on any man unlucky enough to venture into the woods, making him dance himself to death.

Myrtha and the others disappear when they hear footsteps approaching: it’s Albrecht, in mourning, bringing flowers to Giselle’s grave. Giselle appears to Albrecht, who realizes that she has forgiven him his falsehood.

In the meanwhile, the Wilis have found Hilarion. Intent on his death, they lead him on a mad dance, but end up tiring of him and abandon him in the woods.

When Albrecht discovers the presence of the Wilis, Myrtha gives the order to take him into the forest. Sacrificing herself for the one she loves, Giselle dances until sunup to save Albrecht. The glimmer of dawn soon forces Myrtha and the Wilis to flee. Giselle, through this sacrifice, succeeds in freeing Albrecht. In peace, she disappears forever.

(source: https://mag.grandsballets.com/en/magazine/texts/synopsis/ )


Links:

https://northernballet.com/giselle/story 

https://www.giselle-ballet.com/about/story.shtml 

https://www.bolshoi.ru/en/performances/41/libretto/ 

http://joffrey.org/gisellesynopsis 

https://www.sfballet.org/explore/articles/synopsis_giselle 

https://lesballetonautes.com/2016/05/27/giselle-a-plot-summary/ 

https://australianballet.com.au/synopsis/giselle-synopsis 

https://www.abt.org/ballet/giselle/ 

Oh wow thank you for this!  I did not know the story of Giselle but I caught myself smiling when reading this because it makes so much more sense!

Thanks a lot for this I didn't know much about Giselle so I was looking some stuff up and your post helped a lot 

Thank you! I understand the drama so much more now!