A prince is a politician, and a politician pretty much has to be shrewd. So that shouldn't come as a surprise, or even have to be noted.
Call a majestic dragon to whine about her sister. Seems about right for her character.
Dragon cheerfully says she got badly beaten up. I think these two fit each other.
"Troubles abound? Seems fun!"
You know before "testing" him to see if he's worthy for your sister (something I'm sure you could easily find out just by asking your parents as they're acquainted with him), how bout you consider thanking him first for saving your sister and keeping her safe?
Nah, that's not how it works. If a character gets close to the MC, there's a rule that some relative or close friend of that character has to test MC's worth, since the relative or friend is absolutely entitled to control that character's choices, and neither of the two characters actually involved don't have any say about it.
Manga is an honest man or woman's business.
Especially since, "I lied," can be such a badass phrase to toss to turn the situation around and create some legitimate conflict and/or tension.
Recently watched a creative video about the difference between world building and lore building. Characters don't actually know how the world works, even if the author does, and that can be a very effective tool to create plot twists. The same applies to characters lying about how things work.