So. let me get this straight.........
So far, what we know about the crown prince's "mysterious" motivations is:
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1) that the crown prince has a curse that can only be cured by "confining" the FL (.........yeah, they said so in chapter "zero", but don't ask me, I still don't get why, either...);
2) that this curse that the prince has is somehow related to the same red dragon that her ancestor defeated (key word, that her ancestor "purified" with "divine power"), and,
3) that the reason it has to be her (that he confines) is connected to how she can use the power of (probably all) constellation treasures....?
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And I think that's all. Did I miss anything?