I had watched the anime before reading the manga and so the progression of certain events diverges at some point. It should be noted that the manga was still being released following the conclusion of the anime so it can't be helped. The overarching plot is the princes developing to become worthy candidates for the throne, but also a journey of self-growth and love. The cast is very quirky, side characters included, and everyone has their itsy bitsy worries that resolve themselves, usually with some help from Haine, because he's a marvelous tutor.
On the topic of Haine, his character is still very unexplained for my liking, you get tidbits of his past here and there, but it's a shame that Haine doesn't get a major growth arc or much of a neat ribbon to close off his work in the story.
The last pages in the final chapter talk about him continuing to be a Royal Tutor and in the last few chapters we do see him cry with how much his students have grown. Ah, and with the ending it seems that each prince's story concludes as expected, Kai doing military stuff, Bruno teaching at the college, Licht doing business stuff and basically ending racism lolol, and of course, Leonhard earnestly serving as the final king of Granzreich before letting the people govern as a Republic, oh and I did forget Eins's short stint of King time where he's still very unmarried and in my headcanon, being gay with Ernst
The joy of this manga is feeling the familial bond that the characters, be it bloodrelated or not, forge throughout the story and the small silly moments of nonsense that break up the everpresent reminder that one of the King's sons will succeed the throne. It's not a straight march to the finish line, but everyone seems to manage their happiness in the end. It's so bittersweet, because after sticking with these guys for over 100 chapters, I really grew attached to everyone as they served as a reminder to me for how nice it is to love others and be loved.
I did cry a bit knowing that my journey with this manga is over, but I'm sure the princes have plenty in store for their futures.