Responses
I read the novel. So spoilers:
She will end up with Asiel for 2 main reasons:
1. Her feelings for him never disappeared.
2. They cannot live without the other (that includes a certain distance and frequency of meeting). This will be explained later.
Another reason (major spoiler):
The throne is currently heirless after the crown Princess. The branch of the Royal family is Nact by bloodline. Since Sienna is owner of a named (by this point the Royal family does not have a named) she has a right to the throne. To solidify her claim without question, one of the condition is to choose Asiel.
You mean to tell me that there's a cute blond boy that seems like a pure and fun dude that Siena could like and she's STILL probably going to end up with Asiel? Oh no this is like the worst