So, I know it's a but earlier to make a theory, but I have been rereading the prologues and can't shake off this idea. I also believe many may have come to this conclusion, but I will talk anyway.
We have a Three Prologue Introduction, One for Aquila and Lamia, and another with them together.
I will call the first two prologues "The Current Timeline", and the prologue of them together "The Original Timeline".
So, right at the batch, we heard about a legend of a dragon who loved a human, but when the human died, the dragon decided to turn back on time to save the human, but even so the human day a years later anyway. And later on the chapter it says how Aquila, the Second Prince, inherited the same power as the dragon, also about his insane power and abilities.
Then, in the second prologue, I actually noticed it's the aftermath about what is happening know. Because Lamia is stepping down her dukedom for her brother and she says "I thought my planes were over when I heard of father's death". Yes, the father didn't die yet and how she plans to turn into a knight. Later on, we find the reason for it is to go after Aquila for what he did with her brother.
Then, we see a flashback of them together and very friendly with each other, with doesn't makes sense considering Lamia's motivation (that at the time we didn't know, but still).
So, here is my theory: In the Original Timeline, Aquila and Lamia were friends with each other and Aquila had feelings for Lamia (I say that based when he is facing a coffin and holding two rings), but Lamia died an unfortunate death (probably some plotting or something, but surely not a natural death). Aquila, who has the same power as the dragon, decides to go back on time to save Lamia. Now, I can't say how much he goes back in time, so here goes my wild guess is since he was a child.
Because in the Current Timeline, Lamia befriends the First Prince, but also based on Aquila's ability. Aquila is well know in his ability to magic and swordmaster, since he already knew those things in the Original Timeline, there was no need to learn at the same pace again. Most likely, he got even better.
Lamia, for the other had, I am guessing Aquila made a spell on her so she won't remember the Original Timeline. We see this in the beginning of her prologue and in the first chapter, were she is having a dream about a "familiar voice" and wants to meet that voice again.
Anyway, the reason Aquila, probably, is so ruthless is his way to avoid Lamia's death at any cost. I have the feeling that he probably fucked up Lamia's brother hand to avoid something in the future (like, him turning into a knight and dying in battle, making Lamia sad or feeling guilty) and so on. Not that is right of him, but he is surely trying to change the future alone, by his power only. But, by hurting Lamia's brother, it made Lamia want to go after Aquila, something I don't think it was his intention.
I don't think Lamia's memories will trigger just by meeting him again (since I am guessing he turned back until his childhood and Lamia saying she meet the prince once). But since Lamia is chasing after Aquila, at some point, her memories of the Original Timeline will come, etc.
That's mostly it, I just want to talk it out and know what anyone thinks? I know it's too soon since Aquila didn't actually showed up, but after rereading the prologues I got this feeling. If someone could tell me about what they think or personal theories, I would love to hear!