From what I read in the novel, this is a spoiler so warning.
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Aria has royal blood, her mother had a one night stand with a Count who comes from a royal family, meaning that only she can use the hourglass. Asher is on the same boat, his special power is teleportation. That’s why he’s always quick to appear and vanish.
actully in this scene when the princess was questioning Aria, she noticed the hourglass box but in the manhwa she didnt.
I remembered that because I thought that the princess would have tried to figure out what was in the box but she never really questioned it after.
so I guess thats why they took that part out of the manhwa
[spoiler warning]
actually, aria's father is not related to the imperial family, he just drank the holy water because he was thought to be the son of a member of the royal family but was actually the son of the marquis from the kingdom of croa.
this explains why aria can only use her ability once a day, while asher can use his ability multiple times in a day.
I wonder what if someone might get an idea of the use of the hourglass and stole it from her.