It's not Ariel. It's Litia and the MC. He sent her to another world to protect her
Phew okay thank you for that , it was a while ago i read that
Wait what who sent who to another world
What? Are you saying that the MC is from this world? The world she's currently in.
Got this from a youtube thread. its long but oh wel you asked
dont read this.. its a spoiler for this manga....
read at ur own risk
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Turns out, the FL is Libertia’s biological twin sister!
The FL is originally from Libertia’s world and her name is Alicia. Their mother gave birth to a white hair purple eyed girl (Libertia) and a black haired and purple eyed girl (our FL/Alicia). While their mother loved both of them, the mother did come from a pretty shitty family. The emperor hates their family because they were the reason the crown prince’s mother (the woman that the emperor loved) died. So the mother and the kids were pretty much forgotten and ignored. The mother raised the girls. The girls were gifted with a mysterious power (a power that seems to come from the mother). Libertia had a power related to the soul and Alicia had a power related to the spirit. Alicia was born weak, because of that she was separated from Libertia in order to get treatment. Sadly, both girls ended up being experimented on by the real villain of the story: their uncle (who is their mother’s brother). He wanted to use them in order to gain immortality. Apparently by consuming souls he could gain immortality and he needed the twins for that. Alicia was most affected by the experiments, because her body was weaker. Nearing the end of the story, we find out that in order to give Alicia better life, Libertia had moved Alicia’s soul into a different dimension (so our modern world). However, Alicia/our FL, was going to die there so in order to save her, Libertia brought the FL/Alicia back into their original world–which is the novel. We also find out that Libertia did a lot of things in order to save and protect the FL. We find out that the novel was actually created by Libertia, so the FL could read it in the modern world and remain aware of how Libertia is doing. Libertia choose a different FL for the novel though (the OG FL, Alice) because she didn’t want Alicia/Our FL to know about all the sh*t Libertia was going through. The reason the OG FL Alice is so happy and energetic and is named Alice, is because Libertia wanted the OG FL to resemble our FL/Alicia. The book was not only a medium that holds Alicia in their world and connects Libertia to Alicia, but it also allowed Alicia to stay in another world.
The uncle is the reason Libertia has the illness. The flower that blooms after a person dies from that illness is the key to the immortality that he wants. The illness is born from rumors and that’s what is fuelling the illness.
Libertia stays by MC as a soul throughout the novel until the end. MC occasionally gets to talk to Libertia after she recovers some memories. With the help of Spirit Kings at the end, Libertia’s soul was able to be purified and she leaves the MC. 
After crown prince gets interested in MC, he slowly puts MC into his “my” category. CP cares for MC and gets extremely angry when he finds out what the uncle did to her. Unlike the Emperor who pretty much just feels guilty/apologizes and doesn’t take much action throughout the story, the CP prefers to take action rather than apologizing. CP offers the crown prince’s position to MC, but MC refuses. In the end, CP proposed that her child will be the next emperor and she accepts.
Later on, when the FL has gotten married to the ML (the ML is Daniel), they get a baby. The baby is the reincarnation of Libertia and will later become the new emperor.
That's- that's a lot to take in and very interesting, feeling a little bit iffy about the Crown Prince part but that's so interesting. Thank you very much. Also I was on his team the beginning.
Okay theory time! So i heard down the grapevine that Ariel might be related to FL ( Maybe sister) If so...ermm isn't Red hair dude in love with his half sister?